 To provide a strong test of generalization of child learning, the same measures of functional behaviours are coded from videos of child-examiner play interactions recorded in the family home on 2 separate days at Follow-up; this examiner is blind to treatment group, not trained in PRT, and is unfamiliar to the child. Standardized child measures are collected at study entry and Week 24. These include the Autism Diagnostic Observation Schedule, Autism Observation Scale for Infants, Mullen Scales of Early Learning - AGS Edition, Preschool Language Scale-4, and Vineland Adaptive Behavior Scales, 2nd ed. Child and parent questionnaires are also completed at these time points. For both the Treatment group and the Control group, a Service Log is completed to record the services and interventions in which the child is currently participating. This Service Log is updated throughout the duration of the familys participation in our trial. A child and familys data is considered useable as long as the child is enrolled in the study up to and including week 4. If a child and family drop out of the study for any reason prior to their completion of week 4, we will not consider their data to be useable. 