This study aimed to evaluate the effectiveness of a randomized controlled trial of a social skills intervention, the Program for the Education and Enrichment of Relational Skills (PEERS: Laugeson et al. in "J Autism Dev Disord" 39(4): 596-606, 2009), by coding digitally recorded social interactions between adolescent participants with ASD and a typically developing adolescent confederate. Adolescent participants engaged in a 10-min peer interaction at pre- and post-treatment. Interactions were coded using the Contextual Assessment of Social Skills (Ratto et al. in "J Autism Dev Disord" 41(9): 1277-1286, 2010). Participants who completed PEERS demonstrated significantly improved vocal expressiveness, as well as a trend toward improved overall quality of rapport, whereas participants in the waitlist group exhibited worse performance on these domains. The degree of this change was related to knowledge gained in PEERS.