Objectives: To date, no meta-analysis has examined the influence of specific intervention characteristics in the overall effectiveness of school-based interventions measured only with accelerometer devices. Thus, the main purpose of this systematic review and meta-analysis was to evaluate the overall and specific variables of the effectiveness of school-based interventions assessed with accelerometer devices among children aged 5-12 years.Study design: A systematic review and meta-analysis to assess the effectiveness of school-based interventions.Methods: Studies published in English, French and Spanish from five electronic databases between January 2010 and December 2021 were identified. Intervention designs with control group measure that assessed daily moderate-to-vigorous physical activity (MVPA) and sedentary time (ST) with acceler-ometer devices in children aged 5-12 years were included. PROSPERO ID: CRD42022326859.Results: A total of 24 trials comprising of 19,487 children (51.3% girls) were included. Intervention studies were ineffective for improving daily MVPA (Hedges' g = 0.07, 95% confidence interval [CI]-0.03 to 0.17; I2 = 84.80%) but were effective for reducing ST (g =-0.08, 95% CI-0.12 to-0.03; I2 = 20.94%). Also, subgroup analyses for MVPA revealed that when studies had two intervention components (g = 0.21, 95% CI 0.06-0.36; I2 = 77.67%), and high quality (g = 0.12, 95% CI 0.01-0.22; I2 = 88.30%) they were effective.Conclusion: School-based interventions have been effective to reduce children's daily time spent in ST. There is no evidence of overall effectiveness of school-based interventions for enhancing daily MVPA in children. Nevertheless, improving the quality of interventions and interventions with two components are effective to increase students' daily MVPA.(c) 2022 The Royal Society for Public Health. Published by Elsevier Ltd. All rights reserved.