Results of the study suggest three distinct classes of participants: high risk (34 percent, medium risk (54 percent), and low risk (12 percent) based on both the participants’ initial violence scores and their growth of violence over time. In addition, the results indicate significant effects (almost 3 times as large as the effect found in the regular one-class analysis) for the high-risk class but not for the medium- or low-risk classes. The result of this randomization was found not to be ideal and more participants who had the potential to engage in violent behavior in the future should be included in the treatment than the control. However, the program further improves the behavior of the treatment group relative to the control group toward the end of intervention. The Aban Aya Youth Project (AAYP) was a longitudinal efficacy trial designed to compare three interventions: School-community (SC), Social Development Curriculum (SDC), and Health Enhancement Curriculum (HEC). It was implemented in grades 5 through 8 in 12 elementary schools in Chicago and surrounding suburbs. This study was designed on the premise that AAYP might have produced differential preventive effects on different groups of participants. That is, the program may have produced different effects on different clusters of individuals within the same population, which may be missed through conventional group data analysis. The study employs a rigorous and state-of-the-art evaluation methodology (growth mixture modeling techniques) to test various assumptions and to address the issue of possibly missed preventive effects in previous analyses of the AAYP Data. Study participants consisted of 552 African-American boys who participated in AAYP between 1994 and 1998. Tables, figures, and references