This study evaluated the effectiveness of a peer-mediated intervention on joint attention (JA) and social play skills for students with autism spectrum disorder (ASD) using a multiple baseline design. Peer-mediated interventions are an evidence-based practice, but there is limited research on using peers outside of the target student's classroom and using them with severely impacted students. In this study, the research team trained third-grade peers to work with preschoolers with ASD in one-on-one play sessions. JA, parallel play, and common focus play were increased during intervention, while solitary and unoccupied play were decreased. Social validity was high as reported by participants. This study provides promising data for increased inclusion of severely impacted students, with benefits for all students involved.