Background School-based physical activity interventions are considered ideal given their potential to reach most children. They aim to help children reach the recommended guidelines of 60 minutes of moderate-to-vigorous physical activity per day. The Daily Mile is a popular school-based active mile intervention which involves children running or jogging for 15 minutes at least three times a week (x3/wk). Since its inception in 2012, The Daily Mile has been widely promoted and is adopted throughout schools in England and globally. The Daily Mile recommends ten core principles for successful implementation, three of which are key for effectiveness. Studies show mixed effects of The Daily Mile and do not often report implementation of the principles. Measures of physical activity intervention implementation in real-world settings are crucial to identify impact and sustainability.

Methods We created and distributed a quantitative survey to 1717 state-funded primary schools in all Greater London boroughs during September 2020. The survey aimed to identify the number of schools that implement and adhere to The Daily Mile’s ten principles: [1] it is quick (15 minutes); [2] fun; [3] whole school participation; [4] taking place in all weathers; [5] at least 3x/wk during curricular lessons; [6] ideally in the school playground; [7] safe route; [8] simple; [9] run/jog at own pace; [10] no change of clothes or shoes. Principles 1 (quick), 3 (whole school participation), and 5 (x3/wk during curricular lessons) are recommended for effectiveness.

Results By September 2021, we achieved a 21% (n=369/1717) response rate; schools in every London borough completed our survey. A total of 196/369 (53%) schools reported implementing The Daily Mile, but none reported adherence to all ten core principles. Adherence to 6/10 core principles was reported by 54/196 (28%) schools, but the principles varied. Only 19/196 (10%) schools reported adherence to all the three key principles recommended for effectiveness.

Discussion Our findings show that of the state-funded primary schools in Greater London reporting implementing The Daily Mile, adherence was to 6/10 principles. Only one in ten schools reported adhering to all three key principles recommended for effectiveness. An implementation gap exists when The Daily Mile is adopted in the real-world.

Conclusion Differences in implementation of The Daily Mile, and potentially other similar active mile interventions in real-world settings, is likely to challenge the intervention’s intended purpose and has important implications for sustainability and scalability. These implementation gaps limit the potential public health impact.