The proposed project seeks to examine adverse effects of group interventions on adolescents' externalizing behavior. Group interventions represent one of the most economical, convenient, and common solution to adolescent behavior problems, a major dilemma for our society that accounts for the greatest number of referrals to mental health clinics. Findings from program evaluation studies have begun to suggest that these groups unexpectedly increase the externalizing behaviors that they were designed to reduce or prevent. However, research has yet to verify whether these unexpected findings represent a meaningful, significant, and lasting adverse effect on adolescent participants rather than a methodologically-driven empirical artifact. Further research based on a strong research design and longitudinal data is necessary to make this important distinction. This project integrates clinical, developmental, and quantitative approaches to investigate a previously discovered adverse effect of an adolescent group intervention. The current study will draw data from a longitudinal, multi-site randomized controlled trial of the Bridges to High School / Puentes a La Secundria Program, a culturally competent, multicomponent prevention program designed to reduce risk during the middle school transition, which has demonstrated positive effects across an array of outcomes. Data were collected at the beginning of 7th grade, with follow-up data collected at the end of the 7th,8th, 9th, and 12th grade from a sample of primarily low-income Mexican American adolescents and their mothers. These data will allow the opportunity to examine intervention effects on long-term outcomes, trajectories of externalizing behaviors across adolescence, and potential mediators of observed effects, each of which provide critical and unique information on the development and prevention of externalizing problems among adolescents. PUBLIC HEALTH RELEVANCE: This study will examine whether adverse effects of adolescent group interventions, which have been found in 24-29% of evaluation studies, are lasting and clinically significant and seeks to identify the processes that explain them. In addition, this stuy reflects the current priority among researchers to refine innovative prevention strategies that are personalized for optimal use among underserved populations, such as Mexican Americans (MAs), the fastest growing US minority group who face substantial health disparities. Investigating the risk and cultural factors that might influence intervention responses among MA youth is necessary to reduce these disparities and their long-term personal and public health burden and strengthen the public health impact of NIMH-supported research.