Explored the mechanisms by which a well-validated intervention to prevent school failure, suspension, and teenage pregnancy produces its effects, using site-level data from 66 sites involving over 1,000 students participating in national replication of the Teen Outreach Program. Multiple informants provided data on operating characteristics of each site. These were then used to explain differences across sites in levels of success in reducing youth problem behaviors using a pre-post design and a well-matched comparison group. In accord with predictions from developmental theory, middle school sites that promoted student autonomy and relatedness with peers and with site facilitators achieved significantly greater levels of success in reducing problem behaviors. Offering volunteer experiences perceived as teaching middle school students new skills and leaving them real choices about the type of work they did was also linked to program success. Although the program was equally successful with students from a wide range of sociodemographic backgrounds, links of program factors to site-level outcomes were found only for middle school but not high school sites. Implications of these findings for the development of programmatic interventions targeted at adolescents are discussed.