The aim of this study was to determine the prevalence of overweight and obesity in primary school children in Glasgow and to evaluate a pilot activity programme for overweight and obese children. BMI was measured in 1548 children. Overweight, obesity and severe obesity were defined as BMI ≥ 85th, 95th and 98th centile, respectively. Overweight and obese children were then invited to participate in a 10-week school-based activity programme. The programme was evaluated by recording weekly attendance, intensity (using the Children's Effort Rating Scale) and enjoyment (scale 1–10). Focus groups were used to explore the experiences and views of the children, teachers, coaches and parents. Of the 1548 children, 31·4 % were overweight, 19·1 % were obese and 12·4 % were severely obese; 38 % of those invited attended the activity programme. Weekly programme attendance was 83 % (range 56–99 %). Mean enjoyment rating (scale 1–10) was 8 for boys and 9 for girls. The intensity of activity sessions were rated ‘very easy’ by boys and ‘just feeling a strain’ by girls. Common themes emerging from the focus groups related to perceived positive and negative aspects of the programme (fun, concerns about stigmatising children); physical and psychological outcomes (fitter, more confident); and future recommendations (involve parents). In summary, the prevalence of overweight and obesity was high. The activity programme was successful in terms of attendance and enjoyment, and overall views of the initiative were positive and there was compelling support for its continuation.