In spring 2020, U.S. schools universally transitioned to online learning due to the COVID-19 pandemic's onset, thus creating a natural experiment for examining adolescents' risk and resilience during an ongoing school crisis response. This longitudinal study used a daily-diary approach to investigate the role of social support in the link between remote learning and psychological well-being across 64 days among a national sample of adolescents (n = 744; 42% Black, 36% White, 22% Other ethnicity/race; 41% boys; 72% eligible for free/reduced-priced lunch; M[subscript age]=14.60, SD[subscript age]=1.71, age-range = 12-17 years). On days when youth attended remote learning, they reported lower daily positive affect, more daily stress, and higher parent social support. There were no significant differences in the effect of remote learning on affect or stress by race or economic status. On days when youth experienced more parent support, they reported lower daily stress and negative affect and higher daily positive affect. On days when youth experienced more peer support, they reported higher daily positive affect. Overall, the study highlights the impact of pandemic-onset remote learning on adolescents' psychological well-being and emphasizes the need for future research on school crisis contingency planning to address these challenges.