We investigated the between- and within-person longitudinal relationship between perceptions of a caring school climate and mental well-being, and the role of socioeconomic position (SEP) for these constructs among high school students in Norway (N = 1508; 60.7% girls). Using a random intercept cross-lagged panel model, we found positive concurrent associations between perceptions of a caring school climate and mental well-being at both between and within levels, and positive cross-lagged effects at the within-person level from mental well-being to later perceptions of a caring school climate across all time points. SEP was positively associated with mental well-being at time one, and at all time points with perceptions of a caring school climate. The findings suggest that mental well-being is a significant contributor to how Norwegian adolescents subsequently perceive their school context, and underscore the importance of school staff being particularly attentive toward students who struggle with mental health, as well as those with lower SEP.