Social Emotional NeuroScience Endocrinology Theatre is a novel intervention program aimed at improving reciprocal social interaction in youth with autism spectrum disorder (ASD) using behavioral strategies and theatrical techniques in a peer-mediated model. Previous research using a 3-month model showed improvement in face perception, social interaction, and reductions in stress. The current study assessed a 2-week summer camp model. Typically developing peers were trained and paired with ASD youth (8–17 years). Social perception and interaction skills were measured before and after treatment using neuropsychological and parental measures. Behavioral coding by reliable, independent raters was conducted within the treatment context (theatre) and outside the setting (playground). Salivary cortisol levels to assess physiological arousal were measured across contexts (home, theatre, and playground). A pretest–posttest design for within-group comparisons was used, and prespecified pairwise comparisons were achieved using a nonparametric Wilcoxon signed-rank test. Significant differences were observed in face processing, social awareness, and social cognition (P < 0.05). Duration of interaction with familiar peers increased significantly over the course of treatment (P < 0.05), while engagement with novel peers outside the treatment setting remained stable. Cortisol levels rose on the first day of camp compared with home values yet declined by the end of treatment and further reduced during posttreatment play with peers. Results corroborate previous findings that the peer-mediated theatre program contributes to improvement in core social deficits in ASD using a short-term, summer camp treatment model. Future studies will explore treatment length and peer familiarity to optimize and generalize gains. Autism Res 2014,7: 4–16. © 2013 International Society for Autism Research, Wiley Periodicals, Inc.