Continuity and change in children's involvement in bullying was examined across the transition to middle school in relation to externalizing and internalizing behavior problems in fifth grade and peer affiliations in fifth and sixth grades. The sample consisted of 533 students (223 boys, 310 girls) with 72% European American, 25% African American, and 3% Other. Although externalizing and internalizing behavior problems in fifth grade were related to bullying involvement in sixth grade, the prediction of stability and desistance in bullying and victimization status was enhanced by information about students' peer group trajectories. Furthermore, peer group trajectories uniquely explained the emergence of bullying and victimization in middle school.