This study explored five years of results from participants in the Project DATA Comprehensive Treatment Model (CTM) which provided intensive early intervention services to young students with Autism Spectrum Disorders (ASD). Data from up to 69 preschool students were utilized in determining pre-/post-program performance on a variety of outcome measures as well as creating growth trajectories on the same outcome measures using Hierarchical Linear Modeling (HLM). Outcome measures were chosen to represent functioning across developmental domains, receptive language skills, social skills, problem behaviors, and degree of autistic characteristics. Results indicated that there was statistically significant pre-/post-program change on 14 of 17 outcome measures, especially those measures that targeted the areas of deficit common to ASD. HLM results indicated that the chosen outcome measures were sensitive to growth and that significant initial status and rates of growth were found across the majority of the outcome measures. Overall results support the efficacy of the Project DATA CTM for all participants though the rates of growth varied widely across the participants. Further HLM analyses suggested that initial status on the PPVT-III was a substantial predictor of performance on the other outcome measures. A discussion of future research as well as implications for practice concludes the article. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]