The differential effectiveness hypothesis states that programs have greater effects on children with high rates of problem behaviors as opposed to children with very low rates. This investigation examined the differential effectiveness of PeaceBuilders on children identified as low-, medium-, or high-risk for future problems. PeaceBuilders is a schoolwide, universal violence prevention program that is theoretically based. The program attempts to change antecedents that trigger aggressive behavior, reward prosocial behavior, and provide strategies to avoid reinforcing negative behavior. The study design included nine project schools with children in kindergarten through fifth grade. A preliminary analysis of the effectiveness of PeaceBuilders compared children in an initial treatment versus delayed treatment condition. The investigation was interested in four outcomes: teacher-reported aggression and social competence and self-reported aggression and prosocial behavior. Findings indicated that the effects of PeaceBuilders were not universal across risk categories. Significant behavior changes were found for children classified at high risk for future violence at baseline. Universal programs, such as PeaceBuilders seem effective and cost-efficient because they can reach an entire population of children, not just children at risk. These programs can change the school climate, reduce the number of classroom disruptions, and ultimately reduce the total number of children at risk for future violence. References