The two waves of data analyzed were obtained from the International Youth Development Study, a large longitudinal cross-national study of 5,769 youth in the fifth, seventh, and ninth grades in the 2 States. For the classroom samples, just over 73 percent of the students participated. The first wave of data collection was completed in 2002 and the second in 2003; 99 percent of the samples in each State were retained to the completion of the 2003 follow-up. Students completed a self-report survey that assessed a range of risk and protective factors as well as outcome measures that included antisocial behavior. The rates of antisocial behavior were similar for the two States at both time-points; however, there were some differences in the rates of specific types of antisocial behavior; and there were clear differences between the States in students' experiences of school suspension and arrests, with Washington State students being more likely to receive these consequences than Victorian students. School suspension increased the risk of subsequent antisocial behavior in both States. Antisocial behavior in younger years was predictive of the same behavior 12 months later, suggesting the importance of early intervention when antisocial behavior emerges. Modifying student attitudes toward drugs and related behaviors may also reduce subsequent antisocial behavior. Poor family management and family conflict increased the risk of antisocial behavior. Students' belief in moral values and the ability to control emotions in stressful situations provided protection against antisocial behaviors. Implications are drawn for research and practice. 1 table and 48 references