We analyzed developmental changes in outsider behavior, testing whether the likelihood that it turns into bullying or defending over time depends on the individual proneness to feel shame or guilt. Participants were 155 preadolescents (72 boys and 83 girls; (Formula presented.)ageat T1 = 10.74 years). Bullying, defending, and outsider behaviors were assessed twice by peer nominations. Shame- and guilt-proneness were assessed at T1 by a self-report questionnaire. All behaviors appeared quite stable; however, regression analyses revealed that shame and guilt were associated with outsider developmental pathway. In particular, students steadily presented outsider behavior after a 9-month period if they showed low guilt or high shame at T1. Results are discussed in terms of future directions for research and interventions.