This study aimed to evaluate the effect of an anti-bullying intervention programme on peers' attitudes towards bullying and their attempts to solve bully/victim conflicts. An experimental pre-test/post-test design with a control group was used. For secondary school students, positive outcomes were observed at post-test 1 on attitudes and on actual rates of intervention. However, the effects had disappeared at post-test 2. For primary school students, significant differences were found at post-test 2, showing a smaller decline in seeking teacher's help and in heightening students' support for victims. Students' competence to solve bully/victim problems in relation to their general pro-social development is discussed.