Background The Daily Mile is a scheme in which children run/walk for 15 minutes a day, in curriculum time. It has been widely adopted in the UK, and encouraged in a number of policy initiatives. However, there is no robust evaluation to date of its effectiveness for increasing physical activity levels or contributing to reducing obesity rates. As for many complex interventions in complex systems, there are challenges in evaluating impact on the public health.

Aims This project was funded to understand The Daily Mile as a public health intervention, and to develop a study design and methods for an appropriate quasi-experimental evaluation.

Methods The design combined a rapid ethnographic assessment of the adoption and implementation of The Daily Mile in five schools in Lewisham; the development of a logic model for the impact of The Daily Mile on public health; and a scoping of designs and methods for a full evaluation, including mapping The Daily Mile as implemented against the Template for Intervention Description and Replication (TIDieR) framework. Data sources included routine local authority school records; participant observation in schools; interviews with children, teachers and local public health specialists.

Findings At school level, there was no evidence of differential uptake of The Daily Mile by school size or student population. In the schools implementing The Daily Mile, considerable variation was observed in how the scheme was adopted at class level. Teachers valued the scheme for the potential impact on students’ physical activity rates, obesity rates and a range of other outcomes. Potential negative effects derived from the generation of stigmatising discourses around body size (of children and teachers) and lifestyles of local pupils. System complexity included the range of other initiatives schools were involved in (which could be alternatives, or additional), local authority support, and the changing role of the scheme funder (INEOS) in supporting the scheme.

A logic model was developed which mapped the important pathways for stakeholders and hypotheses about the impact of the scheme. Potential sources of secondary data for a full evaluation were identified. Although randomised controlled trials can provide information on how the scheme impacts on outcomes such as physical activity and body weight, they are unlikely to be informative on what the causal conditions are for successful implementation. One promising design for this is Qualitative Comparative Analysis, and a protocol was developed from findings from the rapid ethnography which hypothesised that leadership commitment, and teachers’ perceptions of the importance of fostering physical capital would be necessary, along with the absence of infrastructure constraints such as lack of outdoor space.

Conclusion A useful evaluation of the impact of The Daily Mile on public health could incorporate a substantial qualitative component to better understand the conditions under which the scheme is successfully implemented, alongside a quasi-experimental study of the impact on body weight, using secondary data sources. However, key outcomes of importance (physical activity, fitness, wellbeing) will require primary data to assess change over time.