The purpose of the present study was to evaluate the effect of the Happy 10 programme on the promotion of physical activity, physical growth and development of primary school students, and on obesity control and prevention. Two similar primary schools from one district of Beijing, China were selected, one as an intervention school and the other as a control school. A Happy 10 programme was implemented at least once every school day in the intervention school for two semesters, whereas no intervention was adopted in the control school. The information on energy expenditure and duration of physical activity was collected by a validated 7-day physical activity questionnaire. Height and weight were measured by the trained investigators following standardized procedure. Energy expenditure and intensity of each Happy 10 session were measured by a physical activity monitor. The average energy expenditure and duration of total physical activity per day among students in the intervention school increased significantly from 15.0 to 18.2 kcal kg−1 and 2.8 to 3.3 h, respectively, whereas the figures significantly decreased in the control school. There was a significant difference in change of weight and body mass index between girls in the intervention and control school (2.4 kg vs. 4.6 kg; 0.47 kg m−2 vs. 0.66 kg m−2). The prevalence of overweight and obesity in the intervention school decreased by 0.4–5.6%, as compared with the increase by 0.6–4.5% in the control school. The average energy expenditure and intensity per 10-min session ranged from 25.0 to 35.1 kcal and from 4.8 to 6.2 kcal kg−1 h−1, respectively, in grades 1–5. The Happy 10 programme provides a useful strategy to promote physical activity among school children, and also plays a positive role in building up physical growth and development of girls.