learners of English could successfully assess the grammaticality of V2, they had significantly more difficulty with subject-verb agreement, which is predicted by the bottleneck hypothesis. Cognitive and scientific reasons for the importance of this theory aside, the bottleneck hypothesis can also be of practical benefit as educators can maximize their time and focus on difficult problems in SLA classroom settings rather than placing attention on concepts that can be grasped with relative ease. The cumulative effects hypothesis This hypothesis claims that second-language acquisition may impose extra difficulties on children with specific language impairment (SLI), whose language delay extends into their school years due to deficits in verbal memory and processing mechanisms in comparison to children with typical development (TD). Existing research on individuals with SLI and bilingualism has been limited and thus there is a need for data showing how to support bilingual development in children with SLI. “Cumulative” refers to the combination of the effects of both internal deficits in language learning and external complications in input and experience caused by bilingualism, which could in turn overwhelm the learner with SLI. The theory predicts that bilingual children with SLI will be disadvantaged, falling behind both their monolingual peers with SLI and bilingual peers with TD. Paradis' longitudinal study examined the acquisition of tense morphology over time in children with SLI who are learning English as a second language. The study found that the acquisition profile for children with SLI is similar to those reported for monolinguals with SLI and TD, showing inconsistencies with CEH. This has provided evidence that SLA will not negatively harm children with SLI and could be beneficial. Comparisons with first-language acquisition Adults who learn a second language differ from children learning their first language in at least three ways: children are still developing their brains whereas adults have mature minds, and adults have at least a first language that orients their thinking and speaking. Although some adult second-language learners reach very high levels of proficiency, pronunciation tends to be non-native. This lack of native pronunciation in adult learners is explained by the critical period hypothesis. When a learner's speech plateaus, it is known as fossilization. Some errors that second-language learners make in their speech originate in their first language. For example, Spanish speakers learning English may say "Is raining" rather than "It is raining", leaving out the subject of the sentence. This kind of influence