This study examined the relationship between social withdrawal (isolation and unsociability) and peer victimization by exploring the moderating influences of gender, classroom norms of social withdrawal, individualism, and collectivism. One hundred fifty-eight adolescents (Mage 5 14.11, SD 5 1.10; 46.3% boys) in 7th and 8th grade from Curitiba, Brazil, completed peer assessments of isolation, unsociability, peer victimization, and self-reports of classroom individualism and collectivism. Isolation and unsociability were aggregated into classroom norms. Data were analyzed using multilevel modeling. Isolation and unsociability positively predicted victimization. Unsociability was a positive predictor of victimization in low-unsociability classrooms. Isolation was negatively associated with victimization in low-isolation classes. The relationship between isolation and victimization was weaker in more collectivistic classes. The relationship between unsociability and peer victimization was strongest among boys in classes low in individualism. This study provides further support that social withdrawal has consequences for adolescents’ socioemotional development which vary by classroom context.