This study examined variability in teachers' reported adherence to a school-based violence prevention program, Creating a Peaceful School Learning Environment, and investigated the relations of teacher adherence to teachers' attitudes related to the intervention and students' attitudes about and responses to bullying. The results provide evidence of variation in adherence among teachers and schools and that teachers' attitudes may have affected adherence. Prospective analyses demonstrated dose-effect relations of teacher adherence with students' attitudes about and responses to bullying, particularly their tendency to assist victims. Findings underscore the importance of assessing and promoting adherence for school-based programs, inform the use of self-report to assess teacher adherence, and provide evidence that teachers are important contributors to the success of school-based antibullying interventions. (Contains 5 tables.)