Thirty studies were included. There were four cluster RCTs, 14 RCTs, 11 controlled trials and one cohort pre-post trial. The quality of studies was considered largely strong (15 studies) or moderate (11 studies). Strengths included blinding (where this was possible) and intervention integrity (assurance that the intervention was delivered according to plan). The treatment of randomisation in cluster RCTs was conducted appropriately. Weaknesses included lack of control group and absence of reporting on withdrawals.
In the 21 studies with available effect size measures, sixty-six effect sizes were reported as being less than 0.2 (no effect); 56 were small; 16 were medium; and two were large. The percentage of effect sizes falling into each of the categories by outcome type were: physical outcomes (no effect 57.7%; small 36.5%; medium 5.8%; large 0%); objective physical activity outcomes (no effect 33.3%; small 42.8%; medium 23.8%; large 0%); self-reported physical activity measures (no effect 60%; small 30%; medium 10%; large 0%); nutritional outcomes (no effect 43.7%; small 45.8%; medium 10.4%; large 0%); and knowledge and attitude outcomes (no effect 22.2%; small 33.3%; medium 22.2%; large 22.2%).
Nine studies evaluated interventions targeted solely at girls, which produced mixed results with regard to physical, nutritional and behavioural outcomes.
Further details were reported in the paper.