Background: While demand for youth violence prevention programs increases, the ability of the school-day schedule to accommodate their time requirements has diminished. Viable school-based prevention programs must strike a balance between brevity and effectiveness. This article reports results from an effectiveness trial of a 12-session curriculum-based universal violence prevention program that promotes healthy conflict resolution skills among urban adolescents. Methods: Using a review of program record data and a multisite quasi-experimental study design, we examined the effectiveness of a New York City-based violence prevention program entitled the Violence Prevention project (VPP) optimized to meet school needs. We analyzed survey data from 1112 9th- and 10th-grade students in 13 New York City public high schools across 4 consecutive school years. Both participants and nonparticipants were surveyed. Results: Review of program record data indicated that the program was implemented with acceptable fidelity to the core component structure, and that participant responsiveness to the model was high. Multilevel modeling indicated that VPP participation was protective for academic self-concept and promoted conflict resolution skills. Conclusions: Findings indicate that semester-long violence prevention programs optimized to meet the needs of a typical high school can be effective at promoting healthy conflict resolution skills in urban adolescents.