Background: Despite the rise in childhood obesity there is still a paucity of evidence for effective interventions that engage children and parents sufficiently to make and sustain lifestyle behaviour change. Most approaches in schools use traditional techniques (lessons, additional activity classes) to affect behaviour change.Objectives: To develop a drama-based, school-located obesity prevention programme, that considers both intervention components and the system in which the intervention is delivered and engages children, their families and schools such that supportive environments for behaviour change are created at home and within the schoolMethods: HeLP was developed iteratively using evidence and behavioural theory with a complex systems framework. Three phases of piloting (398 children), involving extensive stakeholder consultation and including an exploratory trial have taken place and an RCT involving 1350 children is underway.Results: Phase 1 and 2 identified the appropriate age group and enabled refinement of intervention messages, activities and modes of delivery. HeLP takes place over 3 school terms and involves four phases; creating a receptive context, the healthy lifestyles week, goal setting and reinforcement activities. In the exploratory trial (4 schools), 24 month measures (anthropometric and behavioural) were obtained from 92% of original cohort. Positive changes were seen in all targeted behaviours in the intervention group. In the control schools the proportion of children overweight/obese rose from 26% at baseline to 32% at 18 and 24 months while, for intervention schools, the proportion remained at baseline levels (24%).Conclusion: HeLP is a dynamic Programme that has been designed to allow for local adaptively, it is feasible to deliver and engages schools, children and families. ‘Proof of concept’ has been established. Its effectiveness, cost effectiveness and an detailed process evaluation are being assessed in a cluster RCT which involves 32 schools and 1350 children.