Early intensive behavioral intervention (EIBI), when delivered through small model programs, has been unequivocally established as an effective treatment for many children with autism. The next major research need is to evaluate the effectiveness of EIBI when delivered to large, community-based samples, since this is how the majority of children access treatment. The present study involved a retrospective analysis of archival data from children who have participated in the EIBI program at St.Amant, in Winnipeg, Manitoba. Similar to findings reported by Perry and colleagues (2008), results showed that children (n = 100) achieved statistically and clinically significant reduction in autism symptom severity, as well as statistically and clinically significant improvement in language skills, adaptive behaviour skills, cognitive level, and rate of development after one year of intervention. Furthermore, when it came to achieving both statistically and clinically significant gains (including more “typical” or normative levels of functioning), children identified as “higher functioning” at intake outperformed “lower functioning” children on all standardized outcome measures. For the smaller subset of children (n = 50) with data available at Intake, Year 1, and Year 2, statistically and clinically significant reductions in autism symptom severity were observed after two years of intervention, as well as statistically and clinically significant improvement in language skills, adaptive behaviour skills, and rate of development. Moderate gains in IQ were also observed, but these gains did not reach statistical significance, perhaps owing to sample size restriction for this measure (n = 11). Across all outcome measures, children identified as “higher functioning” at intake were far more likely to achieve “typical” levels of functioning after two years of intervention. As for predictors of outcome at Year 1, language and cognitive functioning at intake offered the strongest predictive value after one year of intervention. Finally, 13 children (13%) had achieved Best Outcome at Year 1; these children achieved notable gains on all outcome measures, and tended to be less severe diagnostically and much higher functioning at intake. Implications of these findings and directions for future research are discussed.