Are school-based physical activity interventions effective and equitable? A meta-analysis of cluster randomized controlled trials with accelerometer-assessed activity.

The prevalence of childhood obesity is increasing at epidemic rates globally, with widening inequalities between advantaged and disadvantaged groups. Despite the promise of schools as a universal context to access and influence all children, the potential of school-based interventions to positively impact children's physical activity behaviour, and obesity risk, remains uncertain. We searched six electronic databases to February 2017 for cluster randomized trials of school-based physical activity interventions. Following data extraction, authors were sent re-analysis requests. For each trial, a mean change score from baseline to follow-up was calculated for daily minutes of accelerometer-assessed moderate-to-vigorous physical activity (MVPA), for the main effect, by gender, and by socio-economic position (SEP). Twenty-five trials met the inclusion criteria; 17 trials provided relevant data for inclusion in the meta-analyses. The pooled main effect for daily minutes of MVPA was nonexistent and nonsignificant. There was no evidence of differential effectiveness by gender or SEP. This review provides the strongest evidence to date that current school-based efforts do not positively impact young people's physical activity across the full day, with no difference in effect across gender and SEP. Further assessment and maximization of implementation fidelity is required before it can be concluded that these interventions have no contribution to make.