Social skills are essential to building empowered and cohesive communities in ethnic diversity. In a world with massive population movements and growing anti-immigrant sentiments, schools stand out as important platforms to instill key social skills into our children to build inter-ethnic cohesion. Achieving this requires the implementation of rigorously tested educational actions. This brief provides the evaluation results of a particular educational program that was implemented in a high-stakes context where the ethnic composition of schools changed abruptly due to a massive refugee influx. The program significantly lowered peer violence and ethnic segregation in schools and improved prosociality in children.