over recent decades there has been increasing research that has provided empirical support for the use of augmentative and alternative communication ( aac ) by children with autism . these children demonstrate pervasive deficits in social communication as well as repetitive and restricted behaviors.1 aac encompasses various modalities that can replace or augment a person s speech and other existing communication skills . these modalities are either unaided , usually in the form of manual signs , or aided , with systems including graphic symbols displayed on communication boards and in books , or devices relying on technology , such as speech generating devices ( sgd ) , including mobile technologies.1 about 30% of children with autism who fail to develop speech skills sufficient for daily communication functions2 and have the most severe disability stand to benefit most from aac.1 these children are at particular risk of developing problem behaviors , limited academic learning , lack of job prospects , poor social networks , and mental health problems as they move from childhood to adulthood.1,3 aided aac , in particular , would seem well suited to individuals with autism because it has been argued that they process visual information more easily than auditory information.4,5 despite the growth of research influencing clinical applications,1 evidence for aac as an autism intervention has been identified as emerging only , rather than established by the national autism centre ( nac)6,7 in the us . emerging interventions are those found by a panel of expert reviewers to be supported by some , but without sufficient high - quality studies indicating their benefits for individuals with autism.6,7 this category contrasts with established interventions for which the nac panel found sufficient high quality , quantity , and consistency of research evidence of treatment effects . of interest was the separate consideration of manual signs ( also rated as emerging ) and visual schedules ( established ) , both of which are considered forms of aac within the field,8,9 and these were reported by wendt and mirenda and brown , respectively . further , there are indications from the autism field that aac has been viewed as having only a limited role ( eg , incorporated only after speech - alone instruction has failed to produce an adequate intervention response , as in the early start denver model10 ) , or no role ( eg , pivotal response training11 ) in some comprehensive intervention programs . a failure to consider the benefits of aac early in a child s comprehensive intervention program is at odds with decades of work from within the aac field . the aim of this work has been to ensure that children with significant communication impairment are provided with communication support as early as possible.12 any attempt to evaluate the role of aac for children with autism and identify future avenues for its efficacious application requires consideration of research from across both aac and autism fields . within each field , research accumulated over the last 40 years has led to an increasing number of systematic reviews in an attempt to synthesize and evaluate the quality of research addressing specific topics . in aac , such synthesis began around 1999 , in an effort to apply evidence - based principles from medicine.13 early reviews by schlosser and lee14 indicated gaps in research quality , particularly in failures to demonstrate generalization and maintenance or social validity ( ie , the practicality of interventions and the social importance of outcomes).15 since then , a number of systematic reviews have been conducted with a specific focus on aac and autism ( eg , ganz1 ) . in autism , similarly , systematic reviews have provided a means to synthesize and evaluate the quality of a large body of intervention research ( eg , howlin et al16 ) , but perhaps none has been as comprehensive as that completed over a number of years by the expert panel of the nac.6,7 our aim was to summarize the systematic reviews in aac of relevance to children with autism to provide a comprehensive overview of the state - of - the - art in this area . along with this , our further aim was to consider the role of aac within the context of established interventions identified by the nac.6,7 in particular , we sought to consider existing and potential points of convergence so as to move both fields forward in addressing the problems with social communication and behavior that impede academic learning by and social inclusion of children with autism . we adopted a combined approach to locate published reviews addressing aac in children with autism , beginning with systematic searches of the databases ovid medline , psycinfo , and eric , and then conducting forward citation and hand searches of reference lists.17 database search terms were autis * or autism spectrum disorders or asd ; aac or augmentative and alternative , or augmentative communication or alternative communication , and limits were from 2000 ( coinciding with the earliest systematic reviews in aac ) to march 2016 , review articles , and papers published in english . after the removal of duplicates , a title and abstract review was conducted , deleting dissertations and book chapters , and other non - peer - reviewed journal publications , and reviews relating to facilitated communication , given that it has been evaluated as a non - evidence - based strategy.6,18 forward citations of early reviews ( n=5 ) yielded two additional reviews , and hand searches of reference lists of later reviews ( n=13 ) yielded eleven more . following title and abstract reviews of retrieved papers , full - text papers were retrieved for 37 articles . two of the authors then independently evaluated the retrieved full text articles against the following inclusion criteria : ( 1 ) a systematic search was conducted ; ( 2 ) the review included one or more effect size metrics , with results reported in either aggregate form or for each included study , and/or a quality appraisal was conducted of included studies ; ( 3 ) studies were of children with autism ( up to 21 years , in line with the nac6,7 ) , or if other participant groups or older individuals were included , results for children with autism could be extracted ; and ( 4 ) all included studies addressed some aspect of the efficacy of aac as an intervention or part of an intervention . we adopted a combined approach to locate published reviews addressing aac in children with autism , beginning with systematic searches of the databases ovid medline , psycinfo , and eric , and then conducting forward citation and hand searches of reference lists.17 database search terms were autis * or autism spectrum disorders or asd ; aac or augmentative and alternative , or augmentative communication or alternative communication , and limits were from 2000 ( coinciding with the earliest systematic reviews in aac ) to march 2016 , review articles , and papers published in english . after the removal of duplicates , a title and abstract review was conducted , deleting dissertations and book chapters , and other non - peer - reviewed journal publications , and reviews relating to facilitated communication , given that it has been evaluated as a non - evidence - based strategy.6,18 forward citations of early reviews ( n=5 ) yielded two additional reviews , and hand searches of reference lists of later reviews ( n=13 ) yielded eleven more . following title and abstract reviews of retrieved papers , full - text papers were retrieved for 37 articles . two of the authors then independently evaluated the retrieved full text articles against the following inclusion criteria : ( 1 ) a systematic search was conducted ; ( 2 ) the review included one or more effect size metrics , with results reported in either aggregate form or for each included study , and/or a quality appraisal was conducted of included studies ; ( 3 ) studies were of children with autism ( up to 21 years , in line with the nac6,7 ) , or if other participant groups or older individuals were included , results for children with autism could be extracted ; and ( 4 ) all included studies addressed some aspect of the efficacy of aac as an intervention or part of an intervention . the aims , type of systematic review and effect size metric ( if used ) , publication period of included studies , inclusion criteria , quality indicator or appraisal method , and key findings were extracted . this information is presented in table 1 , with studies organized according to key themes relating to review aims . these themes were ( 1 ) overall effectiveness of various types of aac and comparison of effectiveness across variables ( n=5 ) ; ( 2 ) evaluation of the aac instructional package , picture exchange communication system ( pecs ) ( n=5 ) ; ( 3 ) effects on speech ( n=2 ) ; ( 4 ) use of high technology , including sgd and newer mobile technologies of ipods , ipads ( n=4 ) ; and ( 5 ) partner instruction ( n=1 ) . most included reviews applied some measure of quality through appraisals that varied in detail : these are summarized in table 2 . these appraisals provided an evaluation of the rigor of studies , thereby indicating the confidence with which outcomes could be attributed to the aac intervention being investigated . across the reviews , most studies were of experimental single case designs ( escd ) , and in fact , seven reviews had this design as an inclusion criterion.19,20,22,2628,36 strategies to address the certainty of the evidence varied . in some reviews , only studies in which experimental control was demonstrated were included , thereby focusing on internal validity , such as through the type of design used.35 in other reviews , studies were categorized according to the extent to which evidence was conclusive.34 more detailed appraisals , such as those based on indicators of quality of escd37 or group studies38 addressed internal validity and aspects of external validity , with indicators taken from horner et al37 including social validity . in five studies , certainty of evidence was not addressed directly19,28,36 or specific design features , such as inclusion of treatment fidelity measures27 or broader indicators , were simply noted.30 information from reviews that did include some form of critical appraisal suggests that only few studies provided conclusive results , with more providing evidence described as preponderant in one coding scheme : that is , based on studies with only minor flaws ( table 2 ) . in some reviews , however , a large proportion of studies were evaluated as providing inconclusive results ( eg , schlosser and koul32 ) . there was debate evident across reviews about the most appropriate means to measure effect size for escd . ganz et al,19,20,28,36 for example , argued that the improvement rate difference index had advantages over the frequently used percentage of nonoverlapping data points , including that it allowed confidence intervals to be determined . regardless of the index used , effect sizes enabled the aggregation of outcomes across studies , as well as a means for evaluating differential effects across variables , which have been reported in table 1 . even taking into consideration concerns about study quality , the evidence presented across reviews , as summarized in table 1 , indicates that , overall , aac has been found to be effective to highly effective for children with autism according to the metrics applied ( table 2 ) . the reviews included favored aided aac , with most evidence supporting the use of pecs , a manualized instructional package for teaching individuals to exchange pictures for desired wants  that is , to learn to request ( described by flippin et al25 )  and sgd ( including newer mobile tablets and other handheld devices ) , with evidence being weaker for other picture - based systems or manual signs . in fact , studies of manual signs were included in systematic reviews only when compared to aided systems.22,26,31,33,34 it has been suggested that manual signs may pose a number of challenges , including being difficult to produce in the presence of motor difficulties and reduced use of gestures and/or poor imitation skills seen in many children with autism.20,42 on the other hand , arguments that aided aac suits strengths in processing visual material26,28 have been made because pictures provide a concrete representation to which a child can refer back.20 this premise was questioned in a recent study , in which it was found that children with autism , unlike children with global developmental delays or without disability,43 did not show improved task performance when asked to complete a series of short instructions under speech + pictures vs speech - only experimental conditions . effectiveness of aac appears overwhelmingly to relate to teaching functional communication , with a focus on requests.20 as shown in table 1 , key targeted outcomes were predominantly requests across the included reviews ; this was particularly the case for studies of pecs , designed to teach requests through picture exchange.25 a tendency to target requests may reflect the relative ease with which they can be taught to children with autism in light of their strengths in behavioral regulation ( ie , communication to gain desired objects or actions , usually through requests ) , as opposed to deficits in social interaction.1 in particular , much research has focused on the efficacy of pecs , designed specifically for children with autism ( table 1 ) . aggregation of data through meta - analysis indicates that the first three stages of pecs are effective to highly effective in teaching children to request preferred items.2427 in stages iv and v of pecs , the use of requests in multiword utterances is targeted , with other communicative functions not introduced until the final stage vi.25 ganz et al28 found large effects for the only two included studies in their review in which all stages were taught , but improvement rate differences ranged from 0.15 to 0.94 , indicating some effects were questionable ( table 2 ) . aac has also been found effective for reducing challenging behaviors.20,21,26,28,29,32,36 interventions reported in table 1 were of functional communication training , in which aac was taught as a replacement behavior.1 in addition , reduction in challenging behavior has been examined as a nontargeted , but rather collateral outcome , again with the rationale that aac would provide a functional behavior as a replacement ( eg , ganz et al28 ) . in many reviews , speech as an outcome , but usually not as a primary target of intervention , was examined . results point mostly to negligible or small effects.25,28,32 the two reviews focused on speech outcomes were motivated by a concern often expressed in aac literature about the potential for aac to impede speech development , as well as a desire to investigate the potential for speech to be enhanced.33,34 these reviews indicate variable outcomes , with schlosser and wendt34 finding that , for individuals with autism , although modest gains in speech could not be attributable directly to aac intervention , there was no evidence of loss of speech skills . the aims , type of systematic review and effect size metric ( if used ) , publication period of included studies , inclusion criteria , quality indicator or appraisal method , and key findings were extracted . this information is presented in table 1 , with studies organized according to key themes relating to review aims . these themes were ( 1 ) overall effectiveness of various types of aac and comparison of effectiveness across variables ( n=5 ) ; ( 2 ) evaluation of the aac instructional package , picture exchange communication system ( pecs ) ( n=5 ) ; ( 3 ) effects on speech ( n=2 ) ; ( 4 ) use of high technology , including sgd and newer mobile technologies of ipods , ipads ( n=4 ) ; and ( 5 ) partner instruction ( n=1 ) . most included reviews applied some measure of quality through appraisals that varied in detail : these are summarized in table 2 . these appraisals provided an evaluation of the rigor of studies , thereby indicating the confidence with which outcomes could be attributed to the aac intervention being investigated . across the reviews , most studies were of experimental single case designs ( escd ) , and in fact , seven reviews had this design as an inclusion criterion.19,20,22,2628,36 strategies to address the certainty of the evidence varied . in some reviews , only studies in which experimental control was demonstrated were included , thereby focusing on internal validity , such as through the type of design used.35 in other reviews , studies were categorized according to the extent to which evidence was conclusive.34 more detailed appraisals , such as those based on indicators of quality of escd37 or group studies38 addressed internal validity and aspects of external validity , with indicators taken from horner et al37 including social validity . in five studies , certainty of evidence was not addressed directly19,28,36 or specific design features , such as inclusion of treatment fidelity measures27 or broader indicators , were simply noted.30 information from reviews that did include some form of critical appraisal suggests that only few studies provided conclusive results , with more providing evidence described as preponderant in one coding scheme : that is , based on studies with only minor flaws ( table 2 ) . in some reviews , however , a large proportion of studies were evaluated as providing inconclusive results ( eg , schlosser and koul32 ) . there was debate evident across reviews about the most appropriate means to measure effect size for escd . ganz et al,19,20,28,36 for example , argued that the improvement rate difference index had advantages over the frequently used percentage of nonoverlapping data points , including that it allowed confidence intervals to be determined . regardless of the index used , effect sizes enabled the aggregation of outcomes across studies , as well as a means for evaluating differential effects across variables , which have been reported in table 1 . even taking into consideration concerns about study quality , the evidence presented across reviews , as summarized in table 1 , indicates that , overall , aac has been found to be effective to highly effective for children with autism according to the metrics applied ( table 2 ) . the reviews included favored aided aac , with most evidence supporting the use of pecs , a manualized instructional package for teaching individuals to exchange pictures for desired wants  that is , to learn to request ( described by flippin et al25 )  and sgd ( including newer mobile tablets and other handheld devices ) , with evidence being weaker for other picture - based systems or manual signs . in fact , studies of manual signs were included in systematic reviews only when compared to aided systems.22,26,31,33,34 it has been suggested that manual signs may pose a number of challenges , including being difficult to produce in the presence of motor difficulties and reduced use of gestures and/or poor imitation skills seen in many children with autism.20,42 on the other hand , arguments that aided aac suits strengths in processing visual material26,28 have been made because pictures provide a concrete representation to which a child can refer back.20 this premise was questioned in a recent study , in which it was found that children with autism , unlike children with global developmental delays or without disability,43 did not show improved task performance when asked to complete a series of short instructions under speech + pictures vs speech - only experimental conditions . effectiveness of aac appears overwhelmingly to relate to teaching functional communication , with a focus on requests.20 as shown in table 1 , key targeted outcomes were predominantly requests across the included reviews ; this was particularly the case for studies of pecs , designed to teach requests through picture exchange.25 a tendency to target requests may reflect the relative ease with which they can be taught to children with autism in light of their strengths in behavioral regulation ( ie , communication to gain desired objects or actions , usually through requests ) , as opposed to deficits in social interaction.1 in particular , much research has focused on the efficacy of pecs , designed specifically for children with autism ( table 1 ) . aggregation of data through meta - analysis indicates that the first three stages of pecs are effective to highly effective in teaching children to request preferred items.2427 in stages iv and v of pecs , the use of requests in multiword utterances is targeted , with other communicative functions not introduced until the final stage vi.25 ganz et al28 found large effects for the only two included studies in their review in which all stages were taught , but improvement rate differences ranged from 0.15 to 0.94 , indicating some effects were questionable ( table 2 ) . aac has also been found effective for reducing challenging behaviors.20,21,26,28,29,32,36 interventions reported in table 1 were of functional communication training , in which aac was taught as a replacement behavior.1 in addition , reduction in challenging behavior has been examined as a nontargeted , but rather collateral outcome , again with the rationale that aac would provide a functional behavior as a replacement ( eg , ganz et al28 ) . in many reviews , speech as an outcome , but usually not as a primary target of intervention , was examined . results point mostly to negligible or small effects.25,28,32 the two reviews focused on speech outcomes were motivated by a concern often expressed in aac literature about the potential for aac to impede speech development , as well as a desire to investigate the potential for speech to be enhanced.33,34 these reviews indicate variable outcomes , with schlosser and wendt34 finding that , for individuals with autism , although modest gains in speech could not be attributable directly to aac intervention , there was no evidence of loss of speech skills . the finding of the nac6,7 that aac is an emerging area , only , appears at odds with the findings from the 17 reviews presented here , even considering differences in publication periods captured : the most recent reviews in table 1 included studies published in 2014;31,32 the nac reviews were completed for two time periods , the first ending 2007,6 and the second covering 20072012.7 the main difference appears to be that studies that incorporated aac as a component or primary part of the intervention were not grouped together as aac interventions , but rather according to the categories of aac devices ( ie , low- and high - tech aids , including sgd , with 14 studies published from 1983 to 2007 included ) , and pecs ( ie , this was treated separately from other aided aac , with 13 studies published from 1994 to 2007 included ) , and sign instruction ( with 11 studies published from 1976 to 2004 included ) . these were all judged to be emerging interventions in the first report,6 with further research reviewed for the second report failing to result in changing the classification for any of these forms of aac to established interventions.7 in the current review , the number of studies judged as lacking rigor or to be of overall poor quality is perhaps further evidence of the emerging status of aac . on the other hand , closer inspection of studies that contributed to classifying some interventions as established in the first nac report6 reveal some included the use of aac as part of intervention protocols . in studies of functional communication training , a type of behavioral package6 ( established ) , for example , were the use of signs and picture systems,44 and high - tech devices45 as replacements for problem ( challenging ) behaviors . schedules , also an established intervention,6 are the use of task lists , often in the form of pictures ( ie , aac ) , to support comprehension and learning within structured activities ( eg , dettmer et al46 ) . finally , studies incorporating aac were also considered by the nac in determining that naturalistic teaching strategies were established.47 regardless of the form of aac used , interventions are multicomponent , with effective implementation requiring considerations beyond the actual modality or system used . hence , although there have been many attempts to compare across types of aac , the system used is part of an intervention only . pictures used in pecs , for example , comprise one component of a comprehensive instructional package that draws on applied behavior analysis ( aba ) , which has a strong research base,6 implemented in a natural context.24 lorah et al31 argued that intervention needs to address both learning how to use these aac systems , including the newer technologies of ipods and ipads , as well as how to communicate effectively and efficiently with them . van der meer and rispoli29 suggested that , in addition to behavioral approaches , greater use of naturalistic strategies that take advantage of incidental teaching moments , environmental arrangement , and following the child s lead might help extend communication to a range of functions beyond requests , including joint attention and social interactions . a concern expressed both in the aac and the autism literature has been the reliance on interventionists highly skilled in the teaching approaches used , resulting in potential problems in translating evidence into real - world settings . tincani and devis,27 for example , suggested that improvements gained through teaching pecs may fail to maintain or generalize to new communication partners and settings once highly skilled researchers , who implement many and complex teaching strategies , have completed their research . only one review focused on training people in a child s social environment to support the use of aac , which indicated varying levels of success across studies.35 some studies did show strong effects , with perhaps greater potential for maintenance than when outcomes rely solely on highly skilled intervention agents , usually researchers . within the autism literature , there is an emerging focus on training parents to implement evidence - based interventions , such as those based on aba , or a combination of aba and naturalistic teaching strategies.48 furthermore , incorporating aac into an approach combining established interventions and delivered by parents has been shown to be effective in improving the communication skills of young children with autism.49 however , as in the aac literature , a recent autism evidence update50 indicated that more research is needed to determine if approaches considered established or emerging by the nac6,7 prove to be as effective when parents are trained to deliver them . a goal of the nac was to provide families , teachers , and other professionals supporting children with autism clear guidance for selecting evidence - based interventions.6,7 this task appears challenging in light of the large and diverse evidence bases in aac and autism , with studies of variable quality , in addition to differences in the role assigned to various forms of aac across the fields . in addition , the heterogeneity evident across children with autism further complicates attempts to take an evidence - based approach to intervention . it has been suggested that there is now sufficient evidence that early and intensive intervention can ameliorate skill deficits and , thereby , ensure that children with autism will enjoy academic success.50 in particular , in the last few years there has been an increase in randomized controlled trials ( rcts ) , considered to provide more robust evidence for both treatment effects and their potential to generalize to the population from which samples have been drawn , than can be provided using escd.50 a review of this more recent research by smith and iadarola50 provides further support for the findings by the nac in terms of interventions considered established , emerging , or questionable.6,7 the extent to which this research base , as well as that for aac , as reviewed here , can inform intervention in real - world settings would seem to be complicated by limitations of even robust research designs . a problem with rcts is the need to obtain homogeneous samples , a challenge that has seen the proliferation of escd in both aac1 and autism50 research . the results of group studies suggest that individual differences across participants may be lost in group means , although measures of variance or the reporting of individual data can reveal that some children may fail to benefit from interventions found effective for others.43 parents and practitioners would benefit from the reporting of subgroup analyses of intervention outcomes so that treatment effects for children with the most complex communication needs can be evaluated . as a result of the extent and complexity of their social , communication , and behavioral needs , these children face challenges in achieving the rapid and consistent progress that may be attainable only by children with lesser difficulties . more detailed reporting of individual variations in intervention performance might avoid masking poor results for children with severe disability . such reporting would provide better indicators of the quality , quantity , and consistency of evidence for intervention effects . individual patterns of learning are readily discernible in escd , an alternative to rcts , and therefore make comparison with a child for whom a practitioner may be considering the intervention an easier task . further , smith and iadarola50 noted that child variables , including preintervention iq , age , functional language , and play , as well as intervention variables , such as treatment intensity or whether pure or eclectic approaches are used , may influence outcomes . it is these potential influences that have relevance in implementing the findings from research reviews to practice . in light of these complex issues use of aac may prove useful when extended beyond the fairly focused aim of teaching basic communication skills , particularly requests.1,29 promises that aac can support ongoing language development12 have yet to be demonstrated convincingly for children with autism , but may be more likely if integrated into comprehensive interventions that combine evidence - based approaches , such as those using aba and naturalistic teaching strategies in everyday contexts , as in pivot response training11 and the esdm.10 developers of the esdm , in suggesting that aac be considered only when a child has failed to demonstrate progress in spoken language,10 may see aac as a last - resort intervention . this approach could increase the potential for learned helplessness , challenging behavior , and missed learning opportunities . in particular , the use of visual supports , and other forms of aac within a child s learning environments , has been suggested as good practice.50 even children who demonstrate increasing spoken language skills stand to benefit from the additional supports that could assist with comprehension and extending language skills . for those who may not make use of visual stimuli for learning,43 providing aac within child - led naturalistic teaching situations is unlikely to impede learning , including of speech.33,34 the underlying tenets of aac research are that communication is multimodal and that individuals differ in terms of those modalities that may best suit their learning needs and preferences.12 the reliance on aided aac has resulted in few studies including sign as a component of instruction or as a communication modality . sign models provided within naturalistic teaching could play a valuable role for children with autism , including extending vocabulary across situations.51 systematic reviews have tended to include only very early manual sign studies6 or those in which signs have been compared to aided systems ( table 1 ) . although some studies have demonstrated better outcomes using aided aac , gevarter et al22 found that ( 1 ) signs combined with speech were more effective than speech alone in increasing communication ; ( 2 ) signs were more likely to result in maintenance and generalization ; and ( 3 ) in comparison to pecs , signs were as effective , while being associated with more vocalizations . such findings demonstrate the value of considering individual differences , both in terms of exploring the evidence base , and making various aac modalities available . the provision of models using both signs and symbols on aids , for example , could maximize the potential to meet individual child learning needs and preferences . furthermore , although it has been suggested that reduced fine motor , gesture , and imitation skills in children with autism may , to some extent , preclude the use of signing,20,42 manual sign instruction may in fact provide a highly salient and ecologically valid communication context in which to target these skills . in light of the potential for individual differences across children with autism to influence the success of both established and emerging interventions , research that provides details of participant characteristics would seem a priority . of the reviews included here , most provided details of children s age and diagnosis , but schlosser and wendt34 included only studies in which participants lacked functional speech , but no information was provided about comprehension ability . in studies included by hart and banda,26 children with autism were described as having limited expressive language , limited speech , being nonverbal , using only 12 word phrases , using a few signs , or demonstrating some vocal imitation prior to intervention . such varied descriptions fail to provide information about possible outcome predictors for children whose communication profiles vary dramatically in terms of underlying linguistic ability and social communication.52 the potential for aac to support ongoing language development is reliant on moving children beyond simple requests . the extent of research into the effectiveness of aac in increasing requests in children with autism seems to warrant a meta - analysis.32 while such a review may further understanding of the most effective and efficient strategies to enhance communication for behavior regulation , there appears to be a greater need to evaluate eclectic teaching strategies in real - world environments that incorporate aac as a means of addressing deficits in social - communication . research into comprehensive and intensive programs , such as the esdm,53 modified by incorporating various forms of aac , would help build evidence for effective intervention for children with variable skill profiles and learning needs.12,43 in this way , aac , when integrated with established interventions , which start early,50 could provide more socially valid outcomes than have been demonstrated to date for children with autism . the finding of the nac6,7 that aac is an emerging area , only , appears at odds with the findings from the 17 reviews presented here , even considering differences in publication periods captured : the most recent reviews in table 1 included studies published in 2014;31,32 the nac reviews were completed for two time periods , the first ending 2007,6 and the second covering 20072012.7 the main difference appears to be that studies that incorporated aac as a component or primary part of the intervention were not grouped together as aac interventions , but rather according to the categories of aac devices ( ie , low- and high - tech aids , including sgd , with 14 studies published from 1983 to 2007 included ) , and pecs ( ie , this was treated separately from other aided aac , with 13 studies published from 1994 to 2007 included ) , and sign instruction ( with 11 studies published from 1976 to 2004 included ) . these were all judged to be emerging interventions in the first report,6 with further research reviewed for the second report failing to result in changing the classification for any of these forms of aac to established interventions.7 in the current review , the number of studies judged as lacking rigor or to be of overall poor quality is perhaps further evidence of the emerging status of aac . on the other hand , closer inspection of studies that contributed to classifying some interventions as established in the first nac report6 reveal some included the use of aac as part of intervention protocols . in studies of functional communication training , a type of behavioral package6 ( established ) , for example , were the use of signs and picture systems,44 and high - tech devices45 as replacements for problem ( challenging ) behaviors . schedules , also an established intervention,6 are the use of task lists , often in the form of pictures ( ie , aac ) , to support comprehension and learning within structured activities ( eg , dettmer et al46 ) . finally , studies incorporating aac were also considered by the nac in determining that naturalistic teaching strategies were established.47 regardless of the form of aac used , interventions are multicomponent , with effective implementation requiring considerations beyond the actual modality or system used . hence , although there have been many attempts to compare across types of aac , the system used is part of an intervention only . pictures used in pecs , for example , comprise one component of a comprehensive instructional package that draws on applied behavior analysis ( aba ) , which has a strong research base,6 implemented in a natural context.24 lorah et al31 argued that intervention needs to address both learning how to use these aac systems , including the newer technologies of ipods and ipads , as well as how to communicate effectively and efficiently with them . van der meer and rispoli29 suggested that , in addition to behavioral approaches , greater use of naturalistic strategies that take advantage of incidental teaching moments , environmental arrangement , and following the child s lead might help extend communication to a range of functions beyond requests , including joint attention and social interactions . a concern expressed both in the aac and the autism literature has been the reliance on interventionists highly skilled in the teaching approaches used , resulting in potential problems in translating evidence into real - world settings . tincani and devis,27 for example , suggested that improvements gained through teaching pecs may fail to maintain or generalize to new communication partners and settings once highly skilled researchers , who implement many and complex teaching strategies , have completed their research . only one review focused on training people in a child s social environment to support the use of aac , which indicated varying levels of success across studies.35 some studies did show strong effects , with perhaps greater potential for maintenance than when outcomes rely solely on highly skilled intervention agents , usually researchers . within the autism literature , there is an emerging focus on training parents to implement evidence - based interventions , such as those based on aba , or a combination of aba and naturalistic teaching strategies.48 furthermore , incorporating aac into an approach combining established interventions and delivered by parents has been shown to be effective in improving the communication skills of young children with autism.49 however , as in the aac literature , a recent autism evidence update50 indicated that more research is needed to determine if approaches considered established or emerging by the nac6,7 prove to be as effective when parents are trained to deliver them . a goal of the nac was to provide families , teachers , and other professionals supporting children with autism clear guidance for selecting evidence - based interventions.6,7 this task appears challenging in light of the large and diverse evidence bases in aac and autism , with studies of variable quality , in addition to differences in the role assigned to various forms of aac across the fields . in addition , the heterogeneity evident across children with autism further complicates attempts to take an evidence - based approach to intervention . it has been suggested that there is now sufficient evidence that early and intensive intervention can ameliorate skill deficits and , thereby , ensure that children with autism will enjoy academic success.50 in particular , in the last few years there has been an increase in randomized controlled trials ( rcts ) , considered to provide more robust evidence for both treatment effects and their potential to generalize to the population from which samples have been drawn , than can be provided using escd.50 a review of this more recent research by smith and iadarola50 provides further support for the findings by the nac in terms of interventions considered established , emerging , or questionable.6,7 the extent to which this research base , as well as that for aac , as reviewed here , can inform intervention in real - world settings would seem to be complicated by limitations of even robust research designs . a problem with rcts is the need to obtain homogeneous samples , a challenge that has seen the proliferation of escd in both aac1 and autism50 research . the results of group studies suggest that individual differences across participants may be lost in group means , although measures of variance or the reporting of individual data can reveal that some children may fail to benefit from interventions found effective for others.43 parents and practitioners would benefit from the reporting of subgroup analyses of intervention outcomes so that treatment effects for children with the most complex communication needs can be evaluated . as a result of the extent and complexity of their social , communication , and behavioral needs , these children face challenges in achieving the rapid and consistent progress that may be attainable only by children with lesser difficulties . more detailed reporting of individual variations in intervention performance might avoid masking poor results for children with severe disability . such reporting would provide better indicators of the quality , quantity , and consistency of evidence for intervention effects . individual patterns of learning are readily discernible in escd , an alternative to rcts , and therefore make comparison with a child for whom a practitioner may be considering the intervention an easier task . further , smith and iadarola50 noted that child variables , including preintervention iq , age , functional language , and play , as well as intervention variables , such as treatment intensity or whether pure or eclectic approaches are used , may influence outcomes . it is these potential influences that have relevance in implementing the findings from research reviews to practice . in light of these complex issues use of aac may prove useful when extended beyond the fairly focused aim of teaching basic communication skills , particularly requests.1,29 promises that aac can support ongoing language development12 have yet to be demonstrated convincingly for children with autism , but may be more likely if integrated into comprehensive interventions that combine evidence - based approaches , such as those using aba and naturalistic teaching strategies in everyday contexts , as in pivot response training11 and the esdm.10 developers of the esdm , in suggesting that aac be considered only when a child has failed to demonstrate progress in spoken language,10 may see aac as a last - resort intervention . this approach could increase the potential for learned helplessness , challenging behavior , and missed learning opportunities . in particular , the use of visual supports , and other forms of aac within a child s learning environments , has been suggested as good practice.50 even children who demonstrate increasing spoken language skills stand to benefit from the additional supports that could assist with comprehension and extending language skills . for those who may not make use of visual stimuli for learning,43 providing aac within child - led naturalistic teaching situations is unlikely to impede learning , including of speech.33,34 the underlying tenets of aac research are that communication is multimodal and that individuals differ in terms of those modalities that may best suit their learning needs and preferences.12 the reliance on aided aac has resulted in few studies including sign as a component of instruction or as a communication modality . sign models provided within naturalistic teaching could play a valuable role for children with autism , including extending vocabulary across situations.51 systematic reviews have tended to include only very early manual sign studies6 or those in which signs have been compared to aided systems ( table 1 ) . although some studies have demonstrated better outcomes using aided aac , gevarter et al22 found that ( 1 ) signs combined with speech were more effective than speech alone in increasing communication ; ( 2 ) signs were more likely to result in maintenance and generalization ; and ( 3 ) in comparison to pecs , signs were as effective , while being associated with more vocalizations . such findings demonstrate the value of considering individual differences , both in terms of exploring the evidence base , and making various aac modalities available . the provision of models using both signs and symbols on aids , for example , could maximize the potential to meet individual child learning needs and preferences . furthermore , although it has been suggested that reduced fine motor , gesture , and imitation skills in children with autism may , to some extent , preclude the use of signing,20,42 manual sign instruction may in fact provide a highly salient and ecologically valid communication context in which to target these skills . in light of the potential for individual differences across children with autism to influence the success of both established and emerging interventions , research that provides details of participant characteristics would seem a priority . of the reviews included here , most provided details of children s age and diagnosis , but only two addressed communication skills of children at the start of intervention . schlosser and wendt34 included only studies in which participants lacked functional speech , but no information was provided about comprehension ability . in studies included by hart and banda,26 children with autism were described as having limited expressive language , limited speech , being nonverbal , using only 12 word phrases , using a few signs , or demonstrating some vocal imitation prior to intervention . such varied descriptions fail to provide information about possible outcome predictors for children whose communication profiles vary dramatically in terms of underlying linguistic ability and social communication.52 the potential for aac to support ongoing language development is reliant on moving children beyond simple requests . the extent of research into the effectiveness of aac in increasing requests in children with autism seems to warrant a meta - analysis.32 while such a review may further understanding of the most effective and efficient strategies to enhance communication for behavior regulation , there appears to be a greater need to evaluate eclectic teaching strategies in real - world environments that incorporate aac as a means of addressing deficits in social - communication . research into comprehensive and intensive programs , such as the esdm,53 modified by incorporating various forms of aac , would help build evidence for effective intervention for children with variable skill profiles and learning needs.12,43 in this way , aac , when integrated with established interventions , which start early,50 could provide more socially valid outcomes than have been demonstrated to date for children with autism . extensive research across the fields of aac and autism provides a strong evidence base to inform decisions about how and when to intervene to ensure optimal communication support for children with autism . yet this evidence base lacks the detail needed to determine the potential for successful outcomes for children with the most significant learning needs , including those who are minimally verbal , following even those interventions with the strongest empirical support . a tendency to ignore the role of aac or relegate it to a last - resort strategy for children who fail to show progress may be a response by autism researchers to an apparent narrow focus of aac research . achieving meaningful changes in the developmental trajectories of children with autism requires comprehensive and intensive approaches that have been based on a solid research foundation . aac has a role in such approaches , but future research that broadens the lens beyond immediate communication targets , while also addressing the learning needs of children with the most severe and complex disabilities is required to converge research across autism and aac fields .
backgroundaugmentative and alternative communication ( aac ) interventions are used for children with autism , often as stand - alone communication interventions for those who are minimally verbal . 
 our aim was to synthesize the evidence for aac interventions for children ( up to 21 years ) , and then consider the role of aac within established , comprehensive , evidence - based autism interventions targeting learning across multiple developmental domains.designwe completed a systematic search of three databases ( ovid medline , psycinfo , eric ) as well as forward citation and hand searches to identify systematic reviews of aac intervention efficacy research including children with autism , published between 2000 and march 2016 in peer - reviewed journals . 
 data pertaining to the quality indicators of included studies , effect sizes for intervention outcomes , and evidence for effectiveness were extracted for descriptive analysis.resultsthe search yielded 17 systematic reviews . 
 most provided indicators of research quality for included studies , of which only relatively few provided conclusive results . 
 communication targets tended to be focused on teaching children to make requests . still , effect size measures for included studies indicated that aac was effective to highly effective.conclusionthere is growing evidence for the potential benefits of aac for children with autism , but 
 there is a need for more well - designed studies and broader , targeted outcomes . 
 furthermore , a lack of evidence for the role of aac within comprehensive intervention programs may account for a tendency by autism researchers and practitioners to neglect this intervention . 
 attempts to compare evidence for aac with other interventions for children with autism , including those in which the use of aac is delayed or excluded in pursuit of speech - only communication , must take into account the needs of children with the most significant learning needs . 
 these children pose the greatest challenges to achieving large and consistent intervention effects , yet stand to gain the most from aac interventions .