Experiences in gender-sexuality alliances (GSAs) could predict youth's academic engagement through improved social-emotional wellbeing (indicated by school belonging, hope, and positive and negative affect). This study utilized three waves of data, each spaced 2-3 months apart, among 627 youth (87% LGBQ+, 45% trans/nonbinary, 48% youth of color) ages 11-22 (M[subscript age] = 15.13) in 51 GSAs in the United States in 2021-2022. Greater peer responsiveness in the GSA predicted increased academic engagement through increased wellbeing overall and specifically through hope and decreased negative affect. Advisor responsiveness and GSA leadership correlated with wellbeing and academic engagement in bivariate analyses but were not predictive in the comprehensive model. GSA experiences were uncorrelated with academic disaffection. Findings suggest how GSAs promote youth's wellbeing and academic engagement.