Children with autism have significant difficulties with social communication, and have particular trouble forming relationships with other children. Social skills interventions are often limited in their ability to teach social interaction skills that can generalize to novel contexts. Given that typically developing siblings spend a significant amount of time with their sibling with autism in a variety of contexts, teaching older siblings to provide intervention to their younger sibling with autism may be an effective method for promoting social skills that can be generalized across social contexts. Sibling-mediated intervention may also have positive effects for the typically developing sibling. Previous research has suggested that reciprocal imitation, in which partners imitate one another in extended turn-taking sequences, is a promising intervention strategy for children with autism. This study will evaluate the efficacy of sibling-implemented Reciprocal Imitation Training (RIT), a naturalistic imitation intervention designed to teach reciprocal imitation skills to children with autism. Researchers will examine whether siblings are able to learn the intervention, and whether the intervention efficiently increases the social-communicative skills in the children with autism. This study will evaluate the effectiveness of both a specific intervention (RIT) and intervention approach (sibling-mediated intervention), which may prove useful in developing social skills in children with autism.