The purpose of this systematic review was to describe single case design (SCD) research studies that systematically included peers in interventions designed to have positive outcomes for children with disabilities aged 3–8 years. Thirty-nine articles published in peer-referred journals in the past 10 years were analyzed in relation to study rigor and characteristics of interventions. Overall, this review supports including peers into systematic interventions for young children with disabilities, as the interventions were effective in producing positive changes in the behavior of young children with a variety of disabilities in social, communication, cognitive, play, and academic skills. No clear pattern emerged of a relationship between ecological factors (setting and interventionist) and generalization and maintenance of child behaviors. The analysis of study rigor suggests that fewer than half of the studies met current standards for SCD research and the number of studies conducting generalization, maintenance, and social validity was inadequate. A significant challenge for the field is to conduct more rigorous research to identify critical factors promoting positive behavior change for young children with disabilities when peers are included in interventions. (author abstract)