Project DATA (Developmentally Appropriate Treatment for Autism) is a school-based comprehensive treatment model for preschool children with autism spectrum disorder (ASD). This study explored 5 years of results from children participating in the model. Data from up to 69 preschool children independently diagnosed with ASD were utilized in determining pre-/post-program performance on a variety of outcome measures representative of functioning across developmental domains, receptive language skills, social skills, problem behaviors, and autism characteristics. Descriptive statistics are utilized to describe the participants at program entry and exit. Results of the paired-samples t tests indicate statistically significant positive program change on 13 of the 16 outcomes measures, especially those that measure core deficits common to ASD. Overall results suggest that Project DATA is a promising practice for providing school-based services to young children with ASD. (author abstract)