["Journal of Research on Adolescence, Volume 36, Issue 2, June 2026. ", "\nAbstract\nThis study explored the co‐developmental trajectories of social behaviors (prosocial behavior, physical aggression, and relational aggression) during early adolescence as well as their relations to environmental antecedents and mental health outcomes. A total of 2587 Chinese students (Mage = 9.61, SD = 0.51; 55.2% boys) completed six measurements at 6‐month intervals. Parallel process latent class growth models identified four heterogeneous patterns: prosocial, stable maladaptive, improving, and dual‐escalating. Multivariate logistic regression analyses revealed that (1) Adolescents who perceived low paternal warmth were more likely to be classified into the dual‐escalating subgroup compared to all other subgroups. (2) Adolescents perceiving low maternal warmth were more likely to belong to the stable maladaptive subgroup rather than the prosocial subgroup. (3) High levels of family emotional abuse and psychological maltreatment by teachers were associated with an increased likelihood of adolescents being classified into the improving and dual‐escalating subgroups, compared to the prosocial and stable maladaptive subgroups. (4) Relatedness need satisfaction at school played a protective role, significantly decreasing the likelihood of adolescents being categorized into any nonprosocial subgroup. Adolescents in the prosocial group showed better mental health, those in the stable maladaptive group demonstrated more frequent depression symptoms and those in the dual‐escalating group exhibited lower self‐esteem. The findings provided insights for prevention and intervention strategies aimed at different patterns of social behaviors during early adolescence.\n"]