BACKGROUND: School-based extracurricular activity participation is one of the primary avenues for prosocial activity engagement during adolescence. In this study, we test the "overscheduling hypothesis" or whether the negative relationship between structured activity intensity (ie, hours) and adolescent bullying and fighting levels off or declines at moderate to high intensity (ie, threshold effects). METHODS: This study uses the Dane County Youth Survey (N = 14,124) to investigate the relationship between school-based extracurricular activity participation intensity and bullying perpetration and physical fighting and whether there are threshold effects of activity participation intensity. RESULTS: The results indicate that there is a negative relationship between extracurricular activity participation intensity and bullying perpetration and physical fighting and that there are threshold effects in these relationships at 3 to 4 hours per week. Results also suggest that low-income adolescents engage in more fighting than other youth and the negative relationship between activity participation intensity and physical fighting was mainly concentrated among low-income adolescents. CONCLUSIONS: School-based extracurricular activity participation--in moderation (ie, up to 3-4 hours per week)--may provide a positive, supportive context that could be a promising prevention strategy for bullying and fighting. Implications for future research on how school-based extracurricular activity participation intensity benefits adolescent functioning are discussed.