In this study, we evaluated three lessons from a manualized social play skills intervention, Play20. Play20 is a focused intervention that is designed to improve early social skill development in children with autism spectrum disorder through naturalistic play. First, we evaluated the procedural fidelity of instructor implementation of Play20, and we also evaluated the effects of an added instructor self-monitoring checklist in further improving instructor behavior. Finally, we evaluated the effects of Play20 on child play outcomes. Instructor procedural fidelity increased in the presence of the Play20 lessons, and further improved in the presence of the instructor self-monitoring checklist. Child outcomes moderately improved as well. Implications and future directions are discussed.