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

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Background

Physical activity is important for children’s mental and physical health, including improved psychological well-being and a lower risk of cardiometabolic diseases. 1,2 The World Health Organization and UK Chief Medical Officers recommend that children should engage in an average of 60 minutes of moderate to vigorous physical activity (MVPA) per day,3,4 and in the UK, government guidelines recommend that 30 minutes of this should take place during the school day. 4 Children spend a large portion of their time at school, and therefore schools play a crucial role in promoting and facilitating physical activity among children.

Children’s physical activity levels vary between schools, with between-school variation, that is unmeasured school-level factors, accounting for 6–18% of the total variance in child daily accelerometer-measured MVPA. 5–8 These between-school differences remain even after adjustment for individual demographics such as age, gender, ethnicity and socioeconomic position, indicating that differences are due to features of the school environment rather than differing pupil demographics. Unmeasured school-level factors are estimated to be responsible for one and a half times more of the variation in children’s MVPA than known individual correlates, such as demographics, active travel and active clubs. 7 Despite this, most studies focus on individual-level factors associated with physical activity,9 resulting in limited evidence on the role of the school environment, such as school policies, curriculum and the physical environment. The existing literature suggests that physical activity is positively associated with policies that support active travel,5,10 school crossing patrol10 and cycle training for children. 11 Aspects of the curriculum can be both positive, such as time spent on physical education (PE), outdoor breaks12 and the use of physical activity in non-PE subjects,11 or negative, such as compromised PE due to lack of space and restriction on access to open space or facilities. 11 Evidence for associations with the physical environment (such as playground equipment and markings) and facilities is mixed,13–15 with much of the research focused on specific contexts, such as active play during breaks, rather than across the full school day, despite current UK guidance, which advocates a ‘whole-school’ approach. 16,17

Lockdowns due to the COVID-19 pandemic have affected both children’s physical activity and the school environment, as schools closed, and children remained at home for large periods of the day. After lockdowns were lifted, children’s physical activity was initially lower than before,18,19 although recent work suggests that MVPA has now recovered to pre-pandemic levels after about a year. 20,21 We also found substantial variation in how the pandemic has affected the school environment, with initial prioritisation of physical activity in the curriculum when schools reopened giving way to pressure to catch up on academic learning, staffing pressures impacting on support for physical activity, and some social distancing policies retained for convenience. 22 These differences in adaptations, policies and provision in schools mean that it is essential to understand between-school variation in children’s physical activity post lockdown, to determine if and how the role of schools has changed, and whether there are key recommendations that can help schools promote physical activity in future.

Aim and objectives

The aim of this report is to explore between-school variation (between-school differences) in children’s physical activity before and after the COVID-19 lockdowns. We will investigate the following:

1. whether the proportion of between-school variation has changed post lockdown, which would indicate a potential change in the role that schools play

2. the extent to which school-level factors explain between-school variation in children’s MVPA and whether this has changed post lockdown.

A secondary aim is to explore whether individual or school-level factors mediate the postlockdown reduction in children’s MVPA.

Methods

The Active-6 study18,20,23 compared postlockdown accelerometer-measured MVPA collected in two waves between May 2021 and July 2022 to a pre-COVID-19 comparator group, to investigate the effects of the COVID-19 lockdowns on the physical activity of children aged 10–11 years (in Year 6 of primary school). Pre-COVID-19 data came from the B-Proact1v study,24 which collected data from 10- to 11-year-old children between March 2017 and May 2018 from 50 schools in and around Bristol, UK. Active-6 invited the same 50 schools to participate, with 23 schools taking part in Wave 1 (May–December 2021) and 27 schools in Wave 2 (January–July 2022); 22 schools participated in both waves. Wave 1 took place when schools had reopened, but some restrictions, such as size of gatherings remained, and there were still disruptions due to COVID-19 outbreaks. Wave 2 took place in 2022 when all restrictions were removed. At all measurement points, we collected child accelerometer and questionnaire data from both children and their parent/carer. Data on a total of 1296 children were collected pre-COVID-19, 393 children in Wave 1 and 436 children in Wave 2 (of whom 128 also participated in Wave 1). Full details of both studies are given elsewhere. 20,24 Both studies received ethical approval from the School of Policy Studies Ethics Committee at the University of Bristol, UK (Ref SPSREC/20-21/150) and parental consent was received for all participants. 25 The project was listed on the Research Registry (project 6646). 26

Results

Individual and school characteristics are summarised by wave in Tables 1 and 2, respectively, with missing values presented in Appendix 1, Table 5. Although fewer schools took part in Waves 1 and 2, demographics were similar. As no schools reported more than five pieces of playground equipment post lockdown, this variable was excluded from subsequent analysis. In addition, we note that active travel policy, school crossing patrol and restrictions on access to open space had larger amounts of missing data (26–34%) and so should be treated with caution.

Between-school variation

A random coefficients model with school-level random-effect terms for each wave was used to compare the percentage of between-school variation across the three waves, which is the percentage of the total variation in child MVPA that can be attributed to school-level factors. A diagonal covariance matrix was found to be sufficient to capture the covariance structure, based on AIC and the log-likelihood ratio test (see Appendix 1, Table 6). A log-likelihood ratio test (p < 0.001) concluded that the school-level wave random coefficients model was a better fit to the data than the random intercepts model (see Appendix 1, Table 6), but that within-school random coefficients for waves were not needed. Total variation in child MVPA was similar between pre-COVID-19 and Wave 2, and slightly lower in Wave 1 (see Appendix 1, Table 7). The percentage of between-school variation (attributable to school-level factors) changed across waves, from 14% pre-COVID-19, dropping to 7% in Wave 1 and increasing again to 13% in Wave 2 (see Figure 1; Appendix 1, Table 7). Figure 2 plots the difference in average MVPA for each school by wave, plotted for those schools with data at all three time points, although estimates of variation are based on data from all schools. Nearly all schools mirrored the overall pattern of an initial drop in average MVPA in Wave 1, followed by a recovery to pre-pandemic levels.

FIGURE 1.

Percentage of unmeasured variation attributable to between-school variation by wave.

FIGURE 2.

Between-school variation in MVPA by wave for wave random coefficients model. Note: Lighter lines plot the average MVPA by school (N = 21 schools with data at all three waves); the darker line indicates the overall average difference. Lines plotted in reference to overall pre-pandemic average (59.9 minutes; red dashed line).

School characteristics that explain between-school variation

Table 3 shows the associations of school characteristics, school-aggregated pupil characteristics, policy, curriculum and environment school factors with child MVPA by adding each variable to the wave random coefficients model separately. The factors identified for the full school characteristics model were school IMD, cycle training policy, compromised PE space, allotments and pitches, plus individual and contextual effects for low IMD, active travel and number of active after-school clubs attended. The potentially relevant variables of an active travel policy and restrictions on access to open space were excluded from this stage due to high levels of missing schools (see Appendix 1, Table 5), but considered later in a sensitivity analysis.

TABLE 3 - Associations between school characteristics, school-aggregated pupil characteristics, policy, curriculum and environment factors and child MVPA

Compared to rarely compromised.

Increase in MVPA for each 10% point increase in school prevalence, for example, from 10% to 20%.

Increase in MVPA for each additional club attended on average in school.

		Estimate	95% CI	N
School characteristics
Year 6 size (per 10 pupils)		0.8	0.0 to 1.5	1777
% in most deprived areas (per percentage point)		−4.0	−9.8 to 1.9	1777
% free meals (per percentage point)		< 0.1	−0.2 to 0.3	1777
Population density (per 10 people/hectare)		0.3	−3.0 to 9.5	1777
School policies
Cycle training policy		5.1	1.2 to 9.1	1641
Written active travel policy		3.6	−0.6 to 7.7	1232
School crossing patrol policy		1.2	−2.9 to 5.2	1332
Restrictions on access to open space		−2.5	−6.7 to 1.8	1353
School curriculum
PE compromised due to spacea: often		−6.5	−12.1 to −0.9	1610
PE compromised due to spacea: sometimes		−2.2	−7.8 to 3.3	1610
PA used in other subjects		3.0	−0.9 to 6.9	1574
Activity breaks during lesson-time		2.7	−1.3 to 6.7	1515
Playground environment
Presence of allotments		4.5	0.9 to 8.1	1777
Presence of assault courses		−1.5	−6.0 to 3.1	1777
Presence of pitches		3.1	−0.5 to 6.8	1777
Presence of drinking fountains		3.0	−1.2 to 7.3	1777
Aggregated contextual effects
Most deprived	Individual	1.313	−2.7 to 5.3	1742
	Contextualb	−1.162	−2.1 to −0.2
Active travel	Individual	5.869	3.9 to 7.9	1735
	Contextualb	1.081	0.3 to 1.9
Screen-viewing (per 10 minutes)	Individual	−0.081	−0.2 to 0.0	1647
	Contextual	−0.343	−1.03 to 0.4
No. clubs attended	Individual	1.606	0.7 to 2.6	1744
	Contextualc	6.566	3.0 to 10.1

The final school characteristics model (Table 4) included additive effects for the presence of a school cycle training policy, compromised PE space and individual and contextual effects for active travel and active after-school clubs. A cycle training policy in the school was associated with 4.0 minutes higher average daily MVPA (95% CI 0.4 to 7.5) for children in that school, compared to children in schools without cycle training. Children in schools where PE was sometimes compromised due to space engaged in an average of 5.4 minutes less MVPA (95% CI 0.5 to 10.2), rising to 9.3 minutes less (95% CI 4.4 to 14.1) when PE was often compromised. Individual-level effects were 6.0 minutes higher MVPA (95% CI 3.8 to 8.1) for a child using active travel, and 1.6 minutes higher MVPA (95% CI 0.5 to 2.6) for each active after-school club attended. Additional contextual effects were seen for attending a school with a higher percentage of pupils using active travel, of 1.0 minute higher MVPA (95% CI 0.3 to 1.7) for each 10% point increase in school active travel prevalence (e.g. from 10% to 20% or from 40% to 50%), and for attending a school where children attended more active after-school clubs, of 7.0 minutes higher MVPA (95% CI 3.5 to 10.5) for each additional club attended on average in the school. Together these factors explained 22% of the between-school variation in child MVPA (i.e. variation attributable to school-level factors) pre-COVID-19, with the proportion more than tripling to 82% at Wave 1 and 72% at Wave 2 (see Figure 3; Appendix 1, Tables 8 and 9). This represented 3%, 6% and 9%, respectively, of the total variation in child MVPA, that is variation attributable to the combination of both school and individual factors (see Appendix 1, Table 9). The relative importance of each school-level factor also changed, with cycle training policy and active travel most important pre-COVID-19, active after-school clubs, active travel and compromised PE space most important in Wave 1 and cycle training policy, active after-school clubs and compromised PE space most important in Wave 2. In a sensitivity analysis we added the variables for a written active travel policy and restrictions on access to open spaces to the model, both of which had a high number of schools missing data. Estimates for the previously included factors were similar (see Appendix 1, Table 10), although with larger confidence intervals and slightly larger estimates for compromised PE space. Restrictions on access to open spaces were additionally associated with 2.3 minutes lower MVPA (95% CI −2.3 to 7.0), compared to children in schools with no restrictions. There was no association with a school active travel policy.

TABLE 4 - Estimates from final school characteristics model (N = 1542)

Increase in MVPA for each 10% point increase in school prevalence, for example, from 10% to 20%.

Increase in MVPA for each additional club attended on average in school.

		Estimate	95% CI
Cycle training policy		4.0	0.4 to 7.5
PE compromised due to space
Sometimes		−5.4	−10.2 to −0.5
Often		−9.3	−14.1 to −4.4
Aggregated contextual effects
Active travel	Individual	6.0	3.8 to 8.1
	Contextuala	1.0	0.3 to 1.7
No. clubs attended	Individual	1.6	0.5 to 2.6
	Contextualb	7.0	3.5 to 10.5
Wave estimates (compared to pre-COVID-19 2017–8)
Wave 1 (2021)		−16.2	−24.8 to −7.6
Wave 2 (2022)		−2.4	−7.3 to 2.6

FIGURE 3.

Between-school variation explained by school characteristics at each wave. Note: Box indicates total amount of between-school variation, while shaded area represents the proportion explained by the variables.

Discussion

While average children’s MVPA differed between schools and across waves, nearly all schools showed the same pattern of an initial drop in Wave 1 and recovery in Wave 2. Moreover, there do not seem to be any systematic patterns to which schools experienced the largest drops in terms of school characteristics. There was no difference in the amount of within-school variation (between- and within-pupil), but between-school variation differed between waves, with the percentage of between-school variation in Wave 1 around half that pre-COVID-19 and in Wave 2 (7% compared to 14/13%). This suggests that in the initial months after restrictions were eased, it was individual factors that dictated a child’s physical activity, with schools only regaining their role as life became more settled by Wave 2. This is not surprising as during the initial period there were still disruptions due to COVID-19 outbreaks, such as school or class closures, and multiple children isolating. We also found no evidence that the initial drop was mediated by either individual- or school-level factors. Although we cannot entirely rule out the explanation that the drop is due to some other unknown factor changing over this time frame, these results support the conclusion that the COVID-19 pandemic and lockdowns led to reductions in children’s physical activity in the shortterm, and that there was little schools could do to mitigate this.

The role of schools remains important after the COVID-19 lockdowns. School factors were responsible for 14% of the total variation in children’s MVPA before COVID-19, consistent with pre-pandemic estimates seen elsewhere,5–8 and returned to a similar level in 2022. Between-school differences in MVPA were explained by the following school factors: whether PE was compromised due to space (often: 9 minutes lower MVPA; sometimes: 5.4 minutes lower), high after-school club attendance (7 minutes higher MVPA for each additional club attended on average in the school), a cycle training policy (4 minutes higher MVPA), and higher prevalence of active travel (1 minute higher MVPA for each increase in 10% points). Individually, these associations of around 5–7 minutes difference in MVPA are moderate in size, representing around 20% of the 30 minutes MVPA recommended during the school day, but could cumulatively contribute to even greater increases, with associated health benefits. For example, replacing 10 minutes of sedentary time with 10 minutes of MVPA is associated with improved cardiometabolic indicators,41 which in turn are associated with lower risk of cardiovascular disease in adulthood. However, there were postlockdown differences in both the overall and relative importance of these factors in describing difference between schools. In Wave 2, these factors explained nearly three-quarters (72%) of all between-school variation, compared to only a fifth (22%) pre-pandemic. This amounts to 9% of the total variation explained post lockdown, which aside from gender, equates to more than any of the individual factors considered (household education, individual club attendance, individual active travel), either separately or combined. There was also a change in which factors were most important in explaining variation between schools, where cycle training and active travel dominated pre-pandemic and cycle training, high active club attendance and compromised PE space most important in 2022. Thus, while the overall importance of the school has not changed, these factors are stronger contributors and have changed in relative importance, suggesting a change in the way in which schools influence children’s physical activity post lockdown. These changes reflect other Active-6 findings, which suggest that although children’s physical activity has recovered to pre-pandemic levels there are notable differences in who is being active and how. 20,42-44 This suggests that understanding the school-specific context is very important for future approaches to increase physical activity at school,45 and that future research should explore the potential of a whole school approach. 17

Pre-COVID-19, while active after-school clubs were important for individual child MVPA, they did not explain between-school differences. This has changed post lockdown, with differences in after-school clubs now accounting for nearly a third (30%) of the between-school variation. This is consistent with other Active-6 results, which found an increased reliance on structured activities, such as clubs post lockdown,43 with a high demand for active school-based clubs that some schools were struggling to meet. 44 The findings in this report reinforce the importance of ensuring schools are able to meet that demand, as the benefits to children include both individual and contextual effects. This means that children benefit not just from attending an after-school club themselves, but from being in a school where children are encouraged or able to attend more active after-school clubs. A child who attends an additional club per week will have an MVPA 1.6 minutes higher on average across the week, but a child who attends a school where on average all the children attend an additional club will have an MVPA 7 minutes higher – even if they do not themselves attend a club. As mentioned above, there are potential health benefits associated with increases in MVPA of this magnitude. We are not aware of any other research that has looked at contextual effects on children’s physical activity, where children benefit both directly from participating in an activity themselves, and indirectly by being in an environment where other children regularly take part, and so further exploration of contextual effects could be a fruitful area of future research. 45 Such factors could be due to a combination of school leadership, culture and/or expectations, as a school that provides lots of clubs that children are encouraged to attend are likely to encourage physical activity in other ways as well. It could also be through the influence of children themselves, with children who attend clubs more active at other times,31 leading to their friends being more active as well,7,46,47 and this in turn shapes the school culture with a higher demand for an active environment. Regardless, it is crucial to ensure that schools are supported in the provision of affordable, and accessible active clubs that are sufficient to meet demand, especially in an increasingly pressured environment. 22

Other positive school factors identified were a cycle training policy and active travel. The importance of a school cycle training policy has nearly doubled, now explaining around a third of the total between-school variation. While previous evidence has shown an association between schools that offer cycle training and higher MVPA,11 other research has found that cycle training did not increase cycling frequency or independent cycling,48 and so it is not clear what is driving this association. Anecdotally, some parents reported that cycle training helped them feel more confident taking their children on bike rides, so cycle training may build confidence and skills and facilitate being more active generally. Cycling was one of the few activities possible during lockdowns, and less crowded roads may have encouraged children to put their training into practice. Cycling infrastructure, both in school (e.g. storage) and out of school (cycle routes), and safety have also been found to be related to active travel to school. 49 In this study, we found that the main benefit of active travel was at the individual level, presumably as it is highly dependent on location, traffic safety and environment as well as individual circumstances. 50,51 There was a small contextual effect of active travel, with 2 minutes higher MVPA for children attending a school with 60% active travel compared to 40%, which may be capturing differences between local neighbourhoods rather than between schools. However, there was no association with a school active travel policy, a reminder that it is the behaviour itself that is associated with MVPA, rather than just the existence of a policy, an important point to consider when recommending a school cycle training policy on the basis of these results.

A negative factor associated with postlockdown differences between schools was if PE lessons were sometimes or often compromised due to space, although this did not explain differences before the pandemic. We note that there was a large change in the number of schools reporting compromised PE sometimes or often before and after lockdowns, from 73% to 13%, respectively, so the role in between-school differences is potentially driven by the few schools where PE is still compromised, which have lower average MVPA. This factor was reported by a member of school staff, and it is possible that this result reflects changes in who answered the questionnaire pre- and post lockdown, although this would have needed to be a systematic change in nearly all the schools in our sample. Alternatively, it could be due to differences in interpretation of the question, with the experience of delivering virtual PE during lockdowns leading to a much wider definition of ‘compromised’, and PE lessons now being seen as less compromised by comparison. It may also be a genuine change, with schools placing more value on physical activity post lockdown22 and thus more likely to prioritise it. Increased options for virtual PE during lockdowns may mean that even when space is an issue, there are now more classroom-based online activities available and so PE can be delivered more effectively in smaller spaces without compromise. The mediation analysis also suggests that the reduction in compromised PE in schools may be responsible for some of the recovery in children’s MVPA to pre-pandemic levels. A related factor is restrictions on access to outdoor space, including the use of rota systems. Unfortunately, missing data makes it difficult to draw firm conclusions, but the study results suggest that such restrictions may be associated with a reduction in MVPA. This is concerning as some schools have reported the continuation of such systems introduced during the pandemic, often for convenience. 22 Access to open space is important for promoting physical activity and lack of sufficient space can impact both on facilitating PE lessons and in managing outdoor free play during play times. 52,53 However, these results show the need to prioritise physical activity even when space is an issue. Schools that use rota systems should ensure that these are in place for the benefit of pupils, rather than for the convenience of the school, and that they facilitate rather than limit physical activity. Those schools that still struggle to deliver PE due to space could explore wider options, such as classroom-based and/or online activities. It may be advantageous to work with schools that have overcome this problem, in order to identify examples of good practice that can be shared.

These findings suggest that post lockdown, the role of schools remains important, but the nature of this role has changed, with cycle training and active clubs being key school-level contributors to explaining difference between schools, along with ensuring that PE lessons are not compromised. It is possible that these are proxies for some other school-level factors that are responsible for differences in MVPA, although there were no strong associations between these factors and any of the extensive range of policies, curriculum and the built environment measures we investigated. They may also reflect a general positive school ethos around physical activity, rather than the presence of these features directly, although a review of the impact of the school physical activity climate on adolescents was inconclusive. 52 However, note that the reverse is also true: not allowing physical activity to be compromised and promoting cycle training, active clubs and active travel are themselves actions that can help build a positive culture around physical activity. The key message is that the focus should be on reducing differences between schools by increasing opportunities for physical activity through a number of different strategies, depending on the school. 45 The study results suggest that a combination of the following could provide a good place to start:

• prioritising physical activity and PE lessons even when space is limited by sharing examples of good practice

• supporting pressured schools to meet the demand for active after-school clubs by offering a wide range of options and encouraging uptake to ensure these are accessible to as many as possible

• offering cycle training to pupils.

These factors are all associated with increases in MVPA of a magnitude that can be linked to improved cardiovascular health in both childhood and adulthood, which suggests that implementing these changes may have the potential to make a substantial public health impact, both in the short- and long-term.

Conclusions

Nearly all schools experienced the same pattern of an initial short-term drop in MVPA followed by a recovery. While schools continue to play an important role in facilitating children’s physical activity, the factors that contribute to this have changed post-COVID-19, with cycle training, active after-school clubs and ensuring PE is prioritised even when space is limited now explaining nearly three-quarters of the between-school differences in children’s MVPA. School-level interventions that focus on these areas and policies that support them offer the potential to increase children’s physical activity.

Additional information

List of abbreviations

AIC

Akaike Information Criterion

IMD

Index of Multiple Deprivation

MVPA

moderate to vigorous physical activity

PE

physical education

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Appendix 1