This study innovatively contributes to the extensive research on student well-being by investigating how social-contextual factors influence students' day-to-day experiences at both the inter- and intra-individual level. Over 10 days, 324 school students aged 15-17 provided twice-daily data on positive affect (PA) and peer relationship quality (PRQ). Data was analysed using Dynamic Structural Equation Modelling. Findings revealed substantial within-person fluctuations in PA (66%). Baseline social support from peers, teachers, and family, as well as momentary PRQ, predicted PA on different levels. Peer social support (PSS) exerted the most significant influence on between-person PA (PSS[subscriptPA] [95% CI] = 0.36, [0.25, 0.47]), followed by teacher social support (TSR). However, neither of the baseline social support factors moderated the PRQ-PA effect (e.g. TSR[subscript[beta]1] [95% CI] = 0.19, [-0.05, 0.41]). This research enhances our understanding of key social-contextual factors influencing daily PA changes in students. Implications, limitations, and suggestions for future research are discussed.