Schools need effective, generalizable, and socially valid social skills interventions to better support the social inclusion and peer relationships of their students on the autism spectrum. We evaluated a Pivotal Response Treatment-based, naturalistic social skills intervention implemented daily by school personnel in reverse inclusion school settings with four students on the autism spectrum (K-2nd grade). Using a single-case experimental design, results indicated that the students on the autism spectrum showed increases in the percent of time engaged in cooperative play with peers during the intervention (p = 0.0026) and moderate changes in social interactions were determined through systematic visual analysis. However, these changes in social behaviors did not generalize to natural inclusive school settings.