Naturalistic developmental behavioral intervention is an emerging class of interventions for young children with autism spectrum disorder. The present article is a meta-analysis of outcomes of group-design studies (n = 27) testing interventions using naturalistic developmental behavioral intervention strategies. Small, significant positive effects of naturalistic developmental behavioral intervention were found for expressive language (g = 0.32), reduction in symptoms of autism spectrum disorder (g = -0.38), and play skills (g = 0.23). Larger effects were found for social engagement (g = 0.65) and overall cognitive development (g = 0.48). A marginal effect was found for joint attention (g = 0.14) and receptive language (g = 0.28). For joint attention, improvement was moderated by hours of professional involvement. Evidence of publication and reporting bias was present for language outcomes. This meta-analysis grows the evidence base for naturalistic developmental behavioral interventions, particularly in the key areas of social engagement and cognition.