Flourishing Adolescents: A Longitudinal Study of School and Peer Support, Social Brain Development, and Positive Affect

Adolescence involves substantial neurodevelopmental and psychosocial changes that shape well-being. This study examined early positive contextual factors that support positive affect, a central indicator of well-being, focusing on school and peer relationships as key adolescent social contexts. Using a large U.S.-based sample (N = 7,879, 47% female) and bivariate latent change score models, we examined longitudinal associations between self-reported school/peer support and MRI-based measures of cortical thickness of social brain regions (medial orbitofrontal cortex (mOFC), supramarginal gyrus (SMG), banks of the superior temporal sulcus (banks of STS), and temporal pole (TP)) from age ~12 to ~14; and how these associations related to positive affect at age ~15. School and peer support were differentially associated with cortical thickness changes and demonstrated sex-specific patterns. We observed correlated change between school support and thickness of the SMG (β = 0.04, p = .01) and TP (β = 0.04, p = .02), as well as female-specific correlated change between peer support and TP thickness (β = 0.05, p < .01), with less steep declines in support associated with less cortical thinning. Although school support at age ~12 was not associated with subsequent cortical thickness change, greater peer support at this age was associated with greater cortical thinning in the SMG (β = -0.05, p < .01) and with a female- specific effect in the mOFC (β = -0.05, p = .02). Additionally, less steep declines in school and peer support were associated with greater positive affect at age ~15 (school: βs = 0.20, ps < .001; peer: βs = 0.07, ps < .001), and less cortical thinning in the SMG was related to greater positive affect (βs = 0.05-0.06, ps < .01). These findings highlight nuanced links between social support, structural cortical development, and positive affect, and underscore the importance of supportive peer relationships and school environments in promoting adolescent socio-emotional development.