The review included 129 studies. The overall number of participants was not reported but most studies included 250 children or more. Follow-up ranged from less than three months (30 studies) to more than 13 months (34 studies). Most studies (65) were of between four and 12 months duration. Frequency of intervention delivery varied from daily to once a week. Health and fitness outcomes were measured in various ways that included body mass index (BMI), motor performance and skin fold thickness. Psychological determinants assessed included attitudes, self-concept, knowledge, motivation and others that included social support.
Twenty-eight studies were judged to be of low methodological quality, 91 were of moderate quality and 10 were considered to be of high methodological quality. Less than half of the studies fulfilled criteria on randomisation, drop-out, blinding of outcome assessment, follow-up and systematic drop-out. Pre-test analysis and timing of measurements were the only domains for which most studies met the criteria. Details of the quality assessment were provided in supplementary material.
Health and fitness outcomes: Seventy-five studies investigated BMI as a health and fitness outcome and 28% found a positive effect of the intervention, 2.7% found a negative effect and 69.3% found no effect. Seventy-four studies investigated physical activity and 56.8% found a positive effect, 6.8% found a negative effect and 36.4% found no effect. Sixty-six studies investigated motor performance and 69.7% reported a positive effect and 30.03% reported no effect. Also investigated were self-concept (20 studies; 30% positive and 70% no effect), knowledge (16 studies; 87.5% positive and 12.5% no effect) and attitudes (16 studies; 43.8% positive, 12.5% negative and 43.7% no effect).
Physical activity behaviour: Seventy-four studies examined physical activity behaviour and 56.8% (42 studies) reported a positive effect of the intervention and five studies (6.8%) reported a negative effect. A positive intervention effect was found in 87.5% of 16 studies investigated knowledge as a psychological determinant. Seven of 16 studies that investigated attitudes reported positive treatment effect and two reported a negative effect. Fourteen studies investigated motivation or enjoyment and four of these found a positive effect of the intervention.
Investigation of sub-categories of studies revealed that studies of adolescents more frequently reported significant differences in BMI between intervention and control group than did studies of children. Studies that combined a physical activity programme with a cognitive approach were more likely to report reduced BMI than studies that investigated an activity intervention only. Low quality studies reported significant results more frequently than studies of moderate or high methodological quality. Long-term studies and studies in which the intervention was delivered more than three times a week reported negative effects on BMI. Further results were reported. Three studies investigated possible psychological moderators. No definitive findings were reported.