Physical activity is known to decrease as children age and with the growing evidence for associations between the school environment and physical activity, the aim of this study was to examine the relationship between school-related factors and changes in physical activity during both school and travel time. As reported previously, only limited changes in activity were observed during time spent at school and the travel period
. However, although the effects were not large, some of the changes that we observed were associated with characteristics of the environment of the school children attended. Overall, more associations were found for sedentary and moderate activity behaviours compared to vigorous physical activity.
During the school day there was evidence that the length of break time may be important in preventing increases in sedentary time and decreases in moderate and vigorous activity, with more favourable outcomes being observed in children attending schools with a break of over 15 minutes. There is evidence that break-time play contributes to overall activity levels in children
, and thus we suggest that children at schools with longer breaks have the opportunity to play more. Counterintuitive associations were recorded with the existence of changing facilities, and play and sports equipment, with the presence of these facilities being associated with detrimental changes in activity. This might in part be due to the fact that only two schools reported providing no play equipment (32 children) and only one no sports equipment (11 children).
Counter-intuitive negative relationships during the school day were also found with the provision of health promotion information and hours of PE. The association with the provision of information may reflect the fact that the information is more likely to be provided in schools with poorer physical activity outcomes. This is in accordance with previous results of a cross sectional analysis in this sample where a negative association was found between the presence of a physical activity policy and vigorous activity
. The association with PE is particularly surprising given that the activity during these lessons should have been recorded by the accelerometry. There is some evidence that the intensity of activity undertaken during PE sessions is surprisingly low
. It may be that these compulsory activities do not result in more active children, particularly if children participating in more PE are less active at other times. After adjustment for all the factors in the models, statistically significant between school ICCs remained for the models of change in school-day physical activity. Although their magnitude was small, this suggests that some factors associated with the school were not accounted for in our models. In particular, we did not assess curriculum-based influences, which may be particularly important for time spent sedentary in the classroom.
When changes in travel time physical activity were considered, there was evidence that the number of same age children at the school was supportive of the maintenance of moderate and vigorous activity and helped prevent adverse changes in sedentary behaviours. Schools with more children were more likely to be located in urban areas, and children attending urban schools have previously been shown to be more likely to walk or cycle
, although the measure of urban–rural status was not significantly associated with change in travel time physical activity in our analysis. One possibility is that more same age children provide better social support for active travel to school, for example by facilitating walking groups or walking with friends. It may also be that some of the physical activity recorded during the travel period was actually from play at either the beginning or end of the journey, and children attending schools with a greater number of friends would be more likely to play. There is evidence that girls attending schools with a greater number of peers have a lower fat mass index
 and this may be associated with higher levels of active play.
Positive associations with physical activity change during the travel period were also found with two measures of safety (a lollypop person, and reporting of safe crossings) which is in accordance with previous research about associations between physical activity and safety on the route to school
[18, 34, 35]. Whether these provisions are actually promoting active travel or whether the provision of these features is associated with the existing prevalence of active travel to school, requires further investigation.
Although some statistically significant associations were detected, it is noteworthy that many of the variables we tested were not found to be associated with changes in the physical activity outcomes we studied. Although the school audit tool we used had been validated and we measured change in physical activity objectively via accelerometers, it is possible that the lack of associations detected could be due to measurement error with our exposures or outcomes. The fact that many of our exposures showed some associations with each other (for example schools that scored badly on one indicator were more likely to score badly on others) could also explain the lack of associations after adjustment. Alternatively, it could indicate the relative unimportance of the school environment as a determinant of change in physical activity in these intensities. We note that a previous study only found associations with the school environment and overall activity in girls, but not with moderate to vigorous physical activity
. This was explained by a possible contribution of the school environment to low intensity activity rather than to activities of moderate to vigorous intensity.
Strengths of this study include the large sample size, and the fact that matched longitudinal data on physical activity and sedentary behaviour change was available for participating children. In addition, change in physical activity was objectively measured using an accelerometer and we made a distinction between behaviours of different intensities. In particular we included sedentary behaviour, which may have an important association with health outcomes
 but which is often not considered alongside physical activity. A further strength is that we used a wide range of methods (questionnaire, audit, GIS) to characterise components of the school environment with a high degree of detail.
There are however a number of weaknesses. For the analyses, school time was defined as the time between 9 am and 3 pm and travel time as the time between 8 and 9 am and between 3 and 4 pm. However, the precise time at which the school day begins and ends will differ by a small amount between schools (median time schools began: 8.50 am, median time schools ended: 3.15 pm) and some of the activity we recorded during these times may have been at home, in the home neighbourhood, or in the school playground rather than on the journey. A further limitation is that, whilst the accelerometry provides a validated measure of activity intensity, it does not tell us what types of activities the children were engaging in. In addition, we did not have confirmation that the children were still attending the same schools at follow-up measurement compared to the baseline measure, although only 47 of the children taking part in SPEEDY-2 changed address and hence it is unlikely that many attended a different school at follow-up. Our measures of school policy were taken at baseline, and we do not know if they may have changed for the children at follow-up. Some of our exposure measures, in particular the provision of sports and play equipment, varied little between schools, limiting our ability to detect associations. Although limited changes in physical activity levels were observed, sufficient heterogeneity in change was available to study associations. A final limitation is that the large number of tests we undertook means that some of the associations we detected may have been due to chance, although we actually found rather few associations given the large number of variables we tested.
In conclusion, this study found a number of school factors to be associated with 1-year changes in physical activity and sedentary behaviours amongst this sample of British children. It appears that the provision of longer breaks, and more safety features on the route to school may help support maintenance of activity levels in children, as may having more same-age peers. The findings suggest how schools have an important role to play in preventing declines in children’s physical activity. Further work is needed to confirm our findings in other settings and investigate the counter-intuitive associations we observed.