Past research demonstrates the promise of multicomponent programs in reducing peer victimization and bullying in older elementary and middle school children, however little research focuses on young children. The current study examines the effectiveness of the WITS Primary program on trajectories of victimization and social responsibility in children in Grades 1 to 3 (n=830). A quasi-experimental design is used to compare schools with well-established programs to nonprogram control schools, using three waves of data collected over 18 months. Children in the WITS program (n=422) showed more rapid declines in peer victimization over time compared with children in control schools (n=418). In addition, teachers of children in program schools reported higher average levels of social responsibility at each time point, compared with control schools. This study adds to support for the multicomponent program in reducing peer victimization among young children. Teachers' important roles in monitoring program implementation are discussed. (Contains 2 tables.)