Bullying behaviors are a growing concern in U.S. schools. We present here a behavioral approach to bully prevention utilizing a schoolwide intervention. Bully prevention in positive behavior support (BP-PBS) teaches students to withhold the social rewards hypothesized to maintain bullying. A single-subject multiple baseline design across 6 students and three elementary schools was implemented in an empirical evaluation of the intervention's effectiveness. Results indicated that implementation was functionally related to decreased incidents of bullying for all 6 students observed. In addition, we observed a decrease in the social responses from victims and bystanders. Finally, school staff implemented the program with a high degree of fidelity and rated the program as effective and efficient. Limitations and implications of these results are discussed. (Contains 2 figures.)