Longitudinal interplay of prosocial behavior and multiple interpersonal relationships among Chinese children in grades 3–6.

= 0.56; 62.2% boys). A random-intercept cross-lagged panel model revealed significant within-person dynamic interactions: a sustained reciprocal enhancement spiral between prosocial behavior and peer relationships (Wave 1-Wave 4) and an early positive feedback loop with family relationships (Wave 1-Wave 3). A critical socialization phase emerged at Grade 4 (Wave 2), when peer relationships positively predicted subsequent family relationships (β = 0.153), prosocial behavior (β = 0.141), and teacher-student relationships (β = 0.110). Family and school interpersonal relationships also facilitated each other. These findings delineate person-environment interactions in social development, extending developmental resource theories and proposing a multisystem interpersonal environment model to inform collaborative family-school interventions. (PsycInfo Database Record (c) 2026 APA, all rights reserved).