This systematic review and meta-analysis examine the effects of school-based mindfulness interventions on psychological outcomes in children and adolescents. A comprehensive search strategy identified 24 studies, of which 13 were published. The studies involved a total of 1348 students, with 876 serving as controls. The overall effect sizes were Hedge's g = 0.40 between groups and g = 0.41 within groups (p < 0.0001). Between-group effect sizes were found in cognitive performance (g = 0.80), stress (g = 0.39), resilience (g = 0.36), and emotional problems (g = 0.19). Third-person ratings showed a moderate effect size (g = 0.25). Mindfulness-based interventions showed promise in improving cognitive performance and resilience to stress. However, the diversity of study samples, implementation methods, and outcome measures require careful examination. The field is still in its early stages, with many studies underpowered and challenges in measuring effects. The review highlights the need for further research to refine interventions and improve their effectiveness. The results suggest that mindfulness-based interventions are feasible and beneficial for children and adolescents, particularly in cognitive performance and resilience. The study also emphasizes the importance of considering the intensity of mindfulness training, as it accounts for a significant portion of the variance in effect sizes. Overall, the findings indicate that mindfulness-based interventions in schools have potential for improving psychological outcomes, but more research is needed to fully understand their effectiveness.This systematic review and meta-analysis examine the effects of school-based mindfulness interventions on psychological outcomes in children and adolescents. A comprehensive search strategy identified 24 studies, of which 13 were published. The studies involved a total of 1348 students, with 876 serving as controls. The overall effect sizes were Hedge's g = 0.40 between groups and g = 0.41 within groups (p < 0.0001). Between-group effect sizes were found in cognitive performance (g = 0.80), stress (g = 0.39), resilience (g = 0.36), and emotional problems (g = 0.19). Third-person ratings showed a moderate effect size (g = 0.25). Mindfulness-based interventions showed promise in improving cognitive performance and resilience to stress. However, the diversity of study samples, implementation methods, and outcome measures require careful examination. The field is still in its early stages, with many studies underpowered and challenges in measuring effects. The review highlights the need for further research to refine interventions and improve their effectiveness. The results suggest that mindfulness-based interventions are feasible and beneficial for children and adolescents, particularly in cognitive performance and resilience. The study also emphasizes the importance of considering the intensity of mindfulness training, as it accounts for a significant portion of the variance in effect sizes. Overall, the findings indicate that mindfulness-based interventions in schools have potential for improving psychological outcomes, but more research is needed to fully understand their effectiveness.