Bullying is a growing public health concern for South Korean adolescents. In our quantitative investigation, we analyze the frequency with which Korean adolescents in single-sex versus coeducational schools are targets of or engage in three peer aggressive behaviors (verbal, relational (social exclusion), and physical (including theft)). We use two nationally representative datasets, the 2011 Trends in International Mathematics and Science Study (TIMSS) and the 2005 Korea Education Longitudinal Study (KELS), and rely on propensity score matching (PSM). For adolescent girls, we find that being in all-girls schools mitigates both their exposure to and engagement in peer victimization. For adolescent boys, we find that boys in all-boys schools have significantly higher odds of experiencing more frequent verbal and physical attacks versus their counterparts in coeducational schools. Our findings strongly suggest that interventions to mitigate peer victimization and aggression in Korea should consider the gendered schooling contexts in which they are implemented.