School-based aggression prevention programs have been implemented in many educational institutions, and fostering the development of social competencies is one of the central aspects of many approaches. The aim of the present study was to assess the level of subjectively perceived usefulness of the prevention program "Faustlos" in connection with the self-reported levels of aggressiveness and social competencies in a sample of German fourth graders. The children had completed the prevention program. Results suggest differences in the level of aggressiveness and social competencies between children with different levels of perceived usefulness of the prevention program.