A repeated cross-sectional study examining the school impact on child weight status.

Objective: The aim of this study is to examine whether there is a differential impact of primary schools upon children's weight status.

Methods: A repeated cross-sectional study was undertaken using five years (2006/07-2010/11) of National Child Measurement Programme data, comprising 57,976 children (aged 4-5 (Reception) and 10-11 (Year 6) years) from 300 primary schools across Devon, England. Examining each year separately, the schools were ranked according to their observed and residual (having accounted for school and neighbourhood clustering and pupil ethnicity and socioeconomic status) school mean body mass index standard deviation score (BMI-SDS). Subtracting the Reception from the Year 6 mean residuals gave 'value-added' scores for each school which were also ranked. The rankings were compared within and across the years to assess consistency.

Results: Although pupil BMI-SDS was high, >97% of the variation in BMI-SDS was attributable to environments other than the school. The 'value-added' by each school was only poorly correlated with the observed and residual pupil BMI-SDS; but none of the rankings were consistent across the five years.

Conclusion: The inconsistency of the rankings and the small variation in BMI-SDS at the level of the school suggests that there is no systematic differential impact of primary schools upon pupil weight status.