<p>Adolescents’ excessive and problematic digital use and its impact on negative wellbeing outcomes are a major concern for researchers, practitioners and families. Although school-based interventions targeting adolescents’ digital use and mental wellbeing may bring behavioral changes and mental wellbeing improvements, their effectiveness is insufficiently understood. This study conducted a pre-registered systematic review and meta-analysis (PROSPERO: CRD420250648902) of school-based interventions among adolescents aged 12–18. Searches across six electronic databases (October 2023; updated February 14, 2025) identified 17 eligible studies, with 11 contributing to meta-analyses, including cluster RCTs, non-randomized trials, and pre–post studies. We applied arm-based random-effects models to report changes from baseline in both digital use and mental wellbeing outcomes. Results show that school interventions are largely effective at reducing screen time relative to the control group, while evidence for problematic digital use is inconclusive. For mental wellbeing, interventions confer advantages for anxiety and depressive symptoms as well as life satisfaction and psychological difficulties, compared to the control group. Sensitivity analyses yield consistent patterns, whereas funnel tests suggest no strong publication bias. Overall, this study indicates that school-level interventions reduce screen time and improve mental wellbeing indicators, while effects on problematic use remain mixed.</p>