This review concluded that school-based obesity prevention programmes resulted in small improvements in body mass index and that much more work is required to establish best practice for obesity prevention in schools. The review had some limitations, but overall the conclusions seem reasonable and appropriately cautious.

To examine the research conducted over a 10-year period on school-based interventions to reduce obesity in children.

PsycINFO, MEDLINE, CINAHL, Academic Search Premier and Cochrane Database of Systematic Reviews were searched for English-language articles published between January 1997 and July 2008. Reference lists of retrieved articles were searched.

Randomised and nonrandomised trials of school-based obesity prevention programmes targeted at children who were normal weight, overweight or at risk for being overweight were eligible for inclusion. Studies needed to report an objective anthropometric outcome measure such as body mass index (BMI) or skinfold thickness. An obesity prevention programme was defined as aiming to decrease cardiovascular risk factors for obesity, increase physical activity or decrease sedentary behaviours. Studies of eating disorder programmes were excluded.

Included studies were diverse and included children from elementary, middle and high school age groups (four to 18 years approximately). Programmes varied in intensity, duration, content, who delivered the intervention and in the extent of parental involvement as well as other characteristics. The main outcome of interest in the review was BMI or BMI Z score.

The authors did not state how the papers were selected for the review.

The authors did not state that they assessed study quality.

The mean difference between intervention and control group in change from baseline to follow-up was extracted and the standardised mean difference (SMD) calculated. Studies were coded for a range of population and intervention moderator variables.

Authors were contacted for further data where necessary.

One reviewer extracted data; 30% were independently extracted by a second reviewer: the level of agreement was high (97.2%).

Studies were pooled in fixed-effect meta-analyses using the r statistic for effect size. Statistical heterogeneity was assessed using the Q statistic. There was an overall pooling of studies. Subgroup analyses were based on the moderator variables. One study was excluded from the analysis due to extreme effect size.

Forty controlled studies that provided 66 comparisons (n=31,059) were included.

There was a small statistically significant benefit with school-based interventions compared to control (r=0.05, 95% CI 0.04 to 0.06); there was statistically significant heterogeneity in this analysis (p<0.001). There were statistically significant between-group differences for several of the moderator variables. More successful interventions were those that were universal (r=0.07, 95% CI 0.05 to 0.08; 37 comparisons), undertaken with four to nine year olds (r=0.06, 95% CI 0.05 to 0.07; 41 comparisons), implemented collaboratively (r=0.12, 95% CI 0.10 to 0.14; 19 comparisons), primarily included children of Asian ethnicity (r=0.30, 95% CI 0.27 to 0.33; five comparisons), encouraged nutritional change (r=0.13, 95% CI: 0.11 to 0.14; 28 comparisons) and sought to reduce sedentary behaviours (r=0.15, 95% CI 0.13 to 0.17; 17 comparisons).

There was a negative effect for short-duration interventions (r=-0.04, 95% CI -0.08 to 0.00; 11 comparisons) and those that implemented system-wide changes in nutrition (r=-0.03, 95% CI -0.04 to -0.01; 15 comparisons).

There was much more work to be done to identify a robust best practice model for obesity prevention in schools. Overall the findings indicated small effects on BMI for school-based obesity prevention programmes and significant variability between studies in outcome.

There was a clearly stated review question. A number of relevant databases were searched. Relevant studies may have been missed as only published English-language studies published during a 10-year period were included. Attempts were made to reduce error and bias in the processes for data extraction; it was unclear whether this was the case for study selection. Study quality was not assessed or taken into consideration in the evidence synthesis or conclusions. It was unclear whether or not the included studies were randomised. Several relevant variables were considered in subgroup analysis and it was appropriate to do so, although the results should be interpreted cautiously as the effect sizes remained small in most subgroups and because of the inherent limitations of such subgroup analyses. Despite these limitations, the authors' overall conclusions seem reasonable and appropriately cautious.

Practice: The authors stated that weight prevention programmes must be carefully planned and suited to each school's population, risk and needs. Goals must include more than BMI reduction or weight loss.

Research: The authors stated that obesity prevention research was required that assessed the efficacy of integrating a holistic body and mind approach with integratal prevention of binge eating and eating disorders. Further analysis was required to explore possible interaction between the moderator variables investigated in the review.

Not stated.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.