This study aimed to investigate how school belonging (SB) mediates the relationship between social support and internalizing/externalizing problems and prosocial behaviors. The research method was descriptive‑correlational. The statistical population comprised secondary school students from Turkey during the 2022‑2023 academic year. A total of 807 students (373 boys and 434 girls), were recruited using convenience sampling to complete the Multidimensional Scale of Perceived Social Support (MSPSS), Psychological Sense of School Membership Scale (PSSM), and Strengths & Difficulties Questionnaire (SDQ). Results indicated that PSS influenced adolescent well-being through SB as a mediator. Family support enhanced school belonging (β = 0.28), which led to lower internalizing (β = -0.40) and externalizing problems (β = -0.27) while increasing prosocial behaviors (β = 0.23). Friend support was directly linked to higher externalizing problems (β = 0.132). Support from significant others strengthened school belonging (β = 0.25) and prosocial behaviors (β = 0.07) while reducing internalizing (β = -0.14) and externalizing problems (β = -0.22). Indirect effects confirmed family and significant other support influenced behavioral outcomes through school belonging, with all indirect effects statistically significant (P < 0.001). These findings underscore the protective role of school belonging, emphasizing its importance in adolescent emotional and behavioral development.