NSCR-Schoolproject is the umbrella for a research program with four partial studies, aimed at enhancing insights into the development of delinquency and other problem behavior of adolescents, and the role of peer network formation among students, psycho-social development, and reactions from the school on problem behavior. The NSCR Schoolproject aimed to enhance insights into the complicated relations between delinquency and other problem behaviors, psycho-social development, peer networks, and school informal interventions. Interview data . In this subproject we analyzed intervention strategies of schools with regard to problem behavior of students. The aim was to assess what schools perceive as problem behavior and how they react on it. Interviews were held with staff members of each school.