Younger and weaker students reported being more exposed to bullying than older students, and boys were most often victims and perpetrators of bullying. In response to the bullying problem, Norway's Ministry of Education launched a school-based intervention program in 1983. The program was based on an authoritative adult-child interaction model and on the existing social environment involving teachers, students, and parents. The program emphasized measures and attitudes characterized by positive teacher and parent involvement, firm limits on unacceptable behavior, and consistent use of noncorporal sanctions for rule violations. An evaluation of the program, based on a quasiexperimental design, involved four adjacent cohorts of 600-700 subjects each from 42 schools. Time-lagged contrasts between age equivalent groups were used to assess program effects. Analysis showed that the frequency of bullying decreased by 50 percent or more during the 2 years following the intervention program. Similar results were obtained for boys and girls and across all grades (four through nine). Program effects were somewhat stronger after 2 years than after 1 year. In addition, the prevalence of such antisocial behaviors as theft, vandalism, and truancy exhibited a substantial decline. At the same time, student satisfaction with school life increased. The nature and causes of bullying are discussed, and the main content of the intervention program and its key principles are described. 38 references, 1 table, and 16 figures