The effectiveness of an existing peer mediation program in a diverse, suburban elementary school was examined. Peer mediation was available to all students (N = 825). Three-year longitudinal data showed significant reductions in the school's out-of-school suspensions after implementation of the peer mediation program. Mediation training also resulted in significant mediator knowledge gains pertaining to conflict, conflict resolution, and mediation, which was maintained at 3-month follow-up. All mediation sessions (N = 34) were successful in resolving conflict, and mediators as well as participants viewed the peer mediation program as valuable. (Contains 4 tables.)