Purpose: This study aims to provide substantive data on the effectiveness of the total-student-body approach to school-based conflict resolution training. The authors investigated the effectiveness of the Peacemakers (D. W. Johnson & Johnson, 1995) program, a total-student-body conflict training program taught bilingually to all students in a K-6 French immersion elementary school in Quebec, Canada. Methodology: A total of 302 Grade K-6 children in a suburban French immersion public elementary school in Quebec, Canada received a conflict resolution training. The training was conducted in French and English. The authors used a correlational design to examine the relation between classroom conflict training and student outcomes, a qualitative data analysis method to determine factors that facilitated or impeded classroom conflict training, and a pretest-posttest comparative design to examine various aspects of student and school impact. Results: The results of the study indicate that, although teachers can reach a moderate level of classroom implementation of conflict training with limited staff development during the first year of adoption, not all teachers will do so. Findings indicate that educators should design teacher professional development on conflict resolution to foster (a) ongoing collaboration for classroom implementation of conflict training, (b) ongoing interaction with those most knowledgeable about conflict resolution, (c) attention to connections between conflict resolution and curriculum content or classroom routines, and (d) ongoing training for deep understanding of conflict resolution. Studies that provide observational-behavioral data on teacher classroom implementations of conflict resolution training are needed to further support (or refute) those program recommendations. Conclusions: The results of the study support the claim that students who are not taught how to manage conflict constructively may never learn to do so. If educators adopt a conflict resolution or peer mediation program as the foundation for a comprehensive school discipline and classroom management system, their challenge will be to teach all students in the school the procedures and skills necessary for resolving their own conflicts constructively, as well as for mediating the conflicts of peers. It is unlikely that cadre approaches to conflict resolution will ever be able to meet that challenge. (Contains 1 note.)