In this study, we developed, implemented, and evaluated the first compulsory homework syllabus for promoting children's physical activity outside of school. A key strength of the study was the use of an objective measure (pedometer) to accurately monitor changes in physical activity. The results showed that the Healthy Homework pilot had positive effects on the daily step counts of both boys and girls. The intervention effect of 2,830 steps.day-1 corresponds to over 25% more activity each day (based on the sample mean pre-intervention). This effect was driven by both an increase of 1,100 steps.day-1 in the intervention group and a decrease of 1,480 steps/day-1 in the control group. While the reasons for the decrease in the control group are unknown, it appears the programme had a protective effect that precluded a similar decrease in the intervention group. Furthermore, the proportion of children achieving step count targets directly related to the prevention of excess body fat (16,000 steps.day-1 for boys, 13,000 steps.day-1 for girls ) increased from 8.6% to 31.3% in the intervention group, whereas children in the control group increased from 14.3% to 16.7%. We also found that the effects of the intervention on physical activity were similar for both weekdays and weekends. This is a noteworthy finding given that children's activity levels tend to diminish during the weekend [20, 22–24]. Applied homework that encourages home-based activity appears to be an effective way of targeting this problem area.
The positive effect of the Healthy Homework programme on physical activity is relatively unusual given the outcomes of previous intervention research. In a comprehensive review of physical activity interventions in children, van Sluijs et al  found that only four of 19 education-based interventions reported significantly positive effects on physical activity. In a similar review, Salmon et al  noted that only one of five 'curriculum only' interventions successfully increased physical activity. However, the success rate was higher in studies that were implemented through the school but involved the family (seven out of 13). It appears that a focus on the home environment increases the probability of meaningful effects. Our promising results may have been due to the emphasis that was placed on increasing physical activity outside of school, including on the weekends.
Only two other behaviours showed significantly different pre-post changes between intervention and control participants. On weekends, vegetable consumption increased by 0.83 servings.day-1 and unhealthy food consumption decreased by 0.56 servings.day-1 as a result of programme participation. The increase in vegetable consumption is noteworthy as it is equivalent to approximately 28% of the daily vegetable recommendation of three servings a day. In addition, an increase of 0.83 servings.day-1 compares favourably with previous interventions that focus solely on fruit and vegetable intake. Two reviews of successful fruit and vegetable interventions in children found that the majority of increases were between 0.2 and 0.6 daily servings [56, 57]. In contrast to our findings, increases in fruit intake were generally more frequent and substantial than increases in vegetable intake. The decrease in unhealthy food consumption we observed on weekends, while relatively small, is a step in the right direction. Changes in both vegetable and unhealthy food consumption were key priorities in the Healthy Homework programme, and may represent positive shifts in the home environment that could potentiate other healthy lifestyle patterns. Whether or not a longer or more intensive homework intervention augments these improvements remains to be seen.
Non-significant effects in the remaining variables targeted in the intervention (screen time, sports participation, active transport to and from school, fruit consumption, and unhealthy drink consumption) suggest that the materials or approaches for these topics may have been insufficient. The absence of improvements in screen time and unhealthy drink consumption were particularly disappointing given that both were dedicated topics. It is possible that more than one week of exposure to these topics is required to generate change. Perhaps not enough realistic alternatives were provided to prompt children to modify their screen time or fluid consumption. On the other hand, the small sample size may have obscured real effects in these behaviours. Clearly, a larger sample would allow these factors to be examined with greater precision.
Another important discovery was that the intervention yielded benefits for boys and girls from a range of socioeconomic backgrounds. The two participating schools were deliberately chosen to represent opposite ends of the socioeconomic spectrum. The similarity of the intervention effects in both schools suggests that it is likely to be beneficial for other primary-level schools, regardless of the socioeconomic rating. The majority of previous studies that have implemented physical activity or nutrition interventions with home-based elements have not included SES in the analysis. Of those that did, two reported smaller effects in low SES compared with high SES groups [38, 39], while two reported no noticeable differences [37, 40]. Nonetheless, it is possible that in the latter studies (and the present one) the similar overall effects on physical activity and/or dietary patterns between SES groups were generated through different pathways. Indeed, there is evidence that families from different socioeconomic backgrounds support their children to be active in different ways . A qualitative comparison of the preferences of homework activities and resources among children and parents from diverse socioeconomic regions could be beneficial in this regard.
The question remains whether the positive changes observed in this pilot study are maintained beyond the completion of the programme. A potential criticism of the programme was the use of wristbands as rewards to increase compliance: a viewpoint common among educators is that the desired behaviour will cease once the reward is removed. We contend that the rewards, in this instance, were used to engage children for the purpose of learning how to be active on their own. While this approach leans towards constructivism - the theory that individuals will generate their own knowledge and understanding from experience - it maintains enough structure that children with little or no understanding of the selected topics are guided towards discovery. The programme aims to create functional knowledge that is taken with the child beyond the completion of the programme, resulting in greater opportunities to be active and promoting lifelong healthy behaviour. Clearly, we cannot comment on the success of this ambition in the present pilot study; however, future studies should consider taking long-term follow-up measures to assess the sustainability of any positive outcomes. Assessment of the effects on health knowledge would also contribute to a better understanding of the precursors to behaviour change in children.
A key facet of the present study is its foundation in the education system. While the goals of the programme are clearly health-related, there are several advantages of operating within the education environment: (1) it is relatively cost-effective to introduce applied homework activities into an existing curriculum, (2) the vast majority of the population can be accessed (all children are required to attend school), and (3) the expertise of trained teachers can be utilised to effectively deliver health-related educational material and instruction. In this study, we developed a homework programme that contributed to all four strands of the Health and Physical Education achievement objectives stated in the New Zealand Curriculum : (1) personal health and physical development, (2) movement concepts and motor skills, (3) relationships with other people, and (4) healthy communities and environments. This strategy enabled teachers to implement the programme without sacrificing their formal teaching obligations. Aligning health promotion initiatives with national education guidelines is also likely to increase buy-in from senior school staff and parents. Another important element of the study was its compulsory nature. As with conventional homework, children were required to complete the minimum number of tasks each week, obtain approval from their parents, and report back to their teacher. This approach was chosen to maximise the level of engagement in the programme, which may explain why significant effects on physical activity and diet were observed in a relatively small sample. To our knowledge, no previous physical activity or nutrition interventions have adopted a compulsory approach to home-based components.
The primary limitation of this study was the small sample size. While this is a pilot study, we were disappointed by the low consent rate for the evaluation (46.3%). Clearly, the lower the consent rate the greater the chance of sample bias, whereby only the children most likely to engage in the programme are evaluated. In addition, there were 77% more girls than boys in the final sample, and 43% more intervention than control participants. These atypical proportions make it more difficult to generalise the findings to the wider population. Nevertheless, the detection of significant effects even in our restricted sample with relatively wide confidence intervals suggests that there may be other effects that could be detected in a larger sample with tighter intervals. Another limitation was the necessity to randomise at the class level. It is probable that a certain amount of class contamination occurred, such that the behaviour of the control participants was affected by the experiences of the intervention participants as they progressed through the programme. Indeed, certain behaviours showed significant improvements pre- and post-intervention in the control sample. While the probability of class contamination does not negate the observed effects of the programme (true effects would be dampened rather than enhanced), it would be preferable for future studies to randomise at the school level. Also, we decided not to request the return of the children's booklets at the completion of the study (in case they were used in future), and consequently we had no record of homework compliance. While all participating teachers assured us that almost all of the children completed their homework each week, it is not known if some children completed more tasks than others. Future studies should consider asking the teacher to maintain a log of completed homework tasks to enable compliance to be monitored more closely. Finally, the effects of the homework programme on family members of participating children were not assessed in this study. Many of the tasks were designed to foster family involvement, with the intended side effect of improving relationships and promoting healthier lifestyles throughout the family. Further research is needed to elucidate these factors.