The concept of the health-promoting school embodies a holistic, whole school approach to personal and community health promotion. Healthy school award schemes, which are increasing, are seen as one way of helping schools to become health promoting. Many are based on the Wessex Healthy Schools Award scheme (WHSA) which was established in 1993. This paper outlines a 3-year evaluation study of the effectiveness of the WHSA intervention in changing health promotion policy and practice in school, and in influencing health-related knowledge, attitudes and behaviour of pupils. The study design was quasi-experimental, and was conducted in 11 intervention secondary and five control schools. It involved pupils, teachers, support staff, parents, school governors, health promotion officers and education advisers, using a range of quantitative and qualitative tools. The Award process, which is linked to nine key areas of health, lasted 15 months. Changes in school health promotion were assessed by audit; pupils' health-related knowledge, attitudes and behaviour through self-administered questionnaires; and attitudes and perceptions of staff, parents and governors from semi-structured interviews. The results showed that audit scores for all areas, except physical activity and taking responsibility for health, increased in intervention schools, indicating positive Award-related changes. There was little improvement in healthy food choices, smoke-free environment and developing community links. Pupils' knowledge, high at the baseline, remained unchanged. Positive effects on smoking uptake and drug use were seen, but little change in healthy eating and physical activity. Older girls made greater progress in all areas. Parents and non-teaching staff strongly supported school health promotion, perceived many benefits of the Award, and wished to be more actively involved. The Award positively influenced the development of a health-promoting school, perceived as an important component of education. Further research is needed into ways of improving pupils' diet and activity levels, how schools can implement a smoke-free environment, the development of community links, and ways in which a whole school approach can be achieved.