A large-scale primary prevention program for wife assault and dating violence was evaluated, employing a measure of attitudes, by means of the London Family Court Clinic Questionnaire on Violence in Relationships. The target audience comprised all students in four high schools. A brief intervention, including a large group presentation on wife assault and dating violence, followed by classroom discussion facilitated by community professionals was instituted. Attitudes, knowledge and behavioral intentions were assessed prior to intervention, immediately afterward, and at five to six weeks postintervention, in a stratified classroom level random sample of the participants. Significant positive attitude, knowledge, and behavioral intention changes were found at posttest, and the majority of these were maintained at delayed follow-up. Striking sex differences were found, with females consistently showing better attitudes than males. A 'backlash' effect was noted among a small number of males after the intervention. It was hypothesized that this group may already be involved in abusive behavior and require secondary, rather than primary, prevention. Students reported a high level of awareness of and experience with violence in their own and their friends' dating and family relationships, and overwhelmingly endorsed primary prevention of relationship violence in the schools.