BACKGROUND:Research trials of early intervention (EI) programs for children with autism spectrum disorder (ASD) generally demonstrate medium-to-large gains, on average, compared with "treatment as usual," in different developmental domains. Almost all children with ASD receive their treatment through community-based services, however, and studies suggest that evidence-based interventions rarely make their way into community practice. Understanding the effectiveness of community-based EI and factors associated with these effects is the first step in developing strategies for wide-scale implementation of effective EI. METHODS:Studies of community-based EI for children with ASD were identified through a systematic search. Changes in cognitive, communication, social, and adaptive functioning from pre-treatment to post-treatment were assessed using standardized mean gain scores. Effect sizes were estimated using random effects models. Moderators of interest included type of community EI program, year of publication, intervention duration, and sample selection. Moderator effects were assessed using analysis of variance of mixed-effects models and meta-regression analyses. RESULTS:Forty-six groups from 33 studies met inclusion criteria (1,713 participants, mean age 37.4 months, 81.1% male). There were small but statistically significant gains in each of the four domains. Hedges's g ranged from 0.21 for adaptive behavior to 0.32 for communication outcomes, after removing outliers and correcting for publication bias. EI programs associated with universities and hospitals were superior, on average, to other community EI programs for cognitive and adaptive behavior outcomes. Intervention duration was negatively associated with effect sizes for communication and adaptive behavior outcomes. CONCLUSIONS:These results indicate that there remains a large gap between outcomes observed in community settings and those reported in efficacy trials.