Introduction Community-based weight management programmes are important in addressing childhood obesity. However, the mechanisms that lead to behaviour change within the programmes are rarely studied within the context of the programmes themselves once they have been implemented. This means that further potential gains in the effectiveness of the programme are often not made and any potential losses of efficacy are often not noticed. Qualitative research alongside randomised controlled trials (RCTs) can tell us the context in which these programmes are implemented and elucidate potential mediators or modifiers of the programmes' effectiveness. The aim of this evaluation is to determine the barriers and enablers to the delivery and impact of an incentive-based behaviour change strategy targeting child obesity to inform future translation.

Methods and analysis Qualitative analysis, including stakeholder and family interviews, focus groups and a survey, will be used. The research will be conducted in collaboration with policymakers, researchers and community health professionals. Participants will be selected from programme providers, and parents/carers and children participating in an Australian community weight management programme during an RCT examining the effectiveness of incentives for improving behaviour change. A maximum variation sampling method based on participant demographics and group characteristics will be used. Thematic analysis will be carried out inductively based on emergent themes, using NVivo V.9.

Ethics and dissemination This research is approved by the South West Sydney Human Ethics Committee review body (HREC/14/LPOOL/480). The evaluation will provide information about the contextual and influencing factors related to the outcomes of the RCT. The results will assist researchers, community health practitioners and policymakers regarding the development, implementation and translation of behaviour change strategies in community initiatives for obese children. Insights gained may be applicable to a range of chronic conditions where similar preventive intervention approaches are indicated.

Trial registration number ACTRN12615000558527, Pre-results.