School-level variation in children's moderate to vigorous intensity physical activity before and after COVID-19: a multilevel model analysis

Schools play a crucial role in facilitating physical activity among children, but the COVID-19 pandemic has affected both children's physical activity and the school environment. It is essential to understand between-school differences in children's physical activity post lockdown, to determine if and how the role of schools has changed. Active-6 is a natural experiment comparing postlockdown accelerometer-estimated physical activity to a pre-COVID-19 comparator group. Accelerometer and individual data were collected on 1296 children aged 10-11 pre-COVID-19 (2017-8), with school characteristics collected from the 50 schools they attended. Post lockdown, we collected accelerometer, individual and school data from 393 children in 23 of the same schools and 436 children in 27 of the same schools in 2021 (Wave 1) and 2022 (Wave 2), respectively. Sources of variation (between-school, between-pupil and within-pupil) in child weekday moderate to vigorous physical activity at each wave were modelled using linear mixed-effects models with school-level wave random coefficients. We extended the model to estimate the proportion of between-school variation explained by school policy, curriculum and physical environment factors and school-aggregated pupil characteristics. We also explored the extent to which postlockdown differences in moderate to vigorous physical activity were mediated by individual or school factors. Between-school variation comprised 13% of the total variation pre-COVID-19, 7% in Wave 1 and 13% in Wave 2. School factors associated with moderate to vigorous physical activity were the following: whether physical education was compromised due to space (often: 9 minutes lower moderate to vigorous physical activity; sometimes: 5.4 minutes lower); high after-school club attendance (7 minutes higher moderate to vigorous physical activity for each additional club attended on average in the school); cycle training policy (4 minutes higher moderate to vigorous physical activity); and higher prevalence of active travel (1 minute higher moderate to vigorous physical activity for each 10% point increase in prevalence). These factors explained 22% of the between-school variation pre-COVID-19, and 72% at Wave 2. The relative importance changed, with cycle training policy and active travel being the most important pre-COVID-19 and cycle training policy, active after-school clubs and compromised physical education space most important in Wave 2. No factors were foun