This report describes the evaluation of a whole-school intervention to improve morbidity and psychosocial well-being in pupils with asthma. In all, 193 children with asthma (7-9 years) from 23 primary/junior schools in the south of England participated. Schools (n = 12) randomly assigned to the intervention group (IV) received a staff asthma training session, advice on asthma policy and practice and an emergency [beta][subscript 2]-agonist inhaler with spacer. Pupils participated in an asthma lesson. Staff and pupils in non-intervention (NI) schools (n = 11) received no asthma-oriented input. While wheeze reports improved for all children with asthma, only the IV group showed lower requirement for medication (P = 0.01), clinically significant improvement (P less than 0.05) in activity related quality of life (QOL) and increased self-esteem (SE: social P = 0.01; athletic P = 0.05; behaviour P = 0.001) in girls. SE decreased for NI girls but there was no change for non-asthmatic peers in NI or IV schools which had similar baseline levels of SE and QOL. There was a marginal improvement in the establishment of asthma policies/practices and no change in school absence or staff knowledge. The significantly increased peer group understanding of asthma seen in the intervention schools may have mediated increased well-being in the IV group. Primary schools are a potentially important context for improving asthma morbidity and psychosocial well-being of children with asthma. (Contains 2 tables and 5 figures.)