Increasing prevalence of childhood obesity calls for comprehensive and cost-effective educative measures in developing countries such as India. School-based educative programmes greatly influence children's behaviour towards healthy living. We aimed to evaluate the impact of a school-based health and nutritional education programme on knowledge and behaviour of urban Asian Indian school children. Benchmark assessment of parents and teachers was also done. We educated 40 196 children (aged 8–18 years), 25 000 parents and 1500 teachers about health, nutrition, physical activity, non-communicable diseases and healthy cooking practices in three cities of North India. A pre-tested questionnaire was used to assess randomly selected 3128 children, 2241 parents and 841 teachers before intervention and 2329 children after intervention. Low baseline knowledge and behaviour scores were reported in 75–94 % government and 48–78 % private school children, across all age groups. A small proportion of government school children gave correct answers about protein (14–17 %), carbohydrates (25–27 %) and saturated fats (18–32 %). Private school children, parents and teachers performed significantly better than government school subjects (P < 0·05). Following the intervention, scores improved in all children irrespective of the type of school (P < 0·001). A significantly higher improvement was observed in younger children (aged 8–11 years) as compared with those aged 12–18 years, in females compared with males and in government schools compared with private schools (P < 0·05 for all). Major gaps exist in health and nutrition-related knowledge and behaviour of urban Asian Indian children, parents and teachers. This successful and comprehensive educative intervention could be incorporated in future school-based health and nutritional education programmes.