The aim of this research is to trial a new version of Happy Homework (HH) on children and parent health outcomes. HH was previously a paper-based 8-week program designed to encourage positive eating habits, physical activity, and healthy sleep routines among children at home. By working together, investigators are aiming make sure HH is easy to use, that it reduces teachers' workload, and enable the students to easily track and engage with HH. We also hope that this will all help contribute to the students meeting 24-hour movement behaviour targets.

Children are invited to participate in the research study. In the study investigators are going to examine children's activity behaviour profiles, and the following measures will be taken:

• Physical activity levels
• Sedentary behaviours
• Sleep duration
• Body mass index (which can be self-reported by the child).

These measures will be conducted at two time-points; (1) 1 week before the intervention begins and (2) 1 week after the intervention. Should children agree to participate in the study; children will wear an accelerometer on their non-dominant wrist and a small device on their right thigh for 8 consecutive days at both time points, along with having their height and weight recorded (the child can self-report this information).

The purpose of this study is to implement a new version of Happy Homework (HH). Within this study the HH app will be trialled, using a cluster-randomised control trial (cluster-RCT) design, to determine its effectiveness, feasibility, and acceptability upon child health outcomes, underpinned by the 24-hour movement guidelines. HH was previously an 8-week school-based home-focussed intervention centred on the promotion of primary school children's positive dietary habits, engagement in physical activity (PA) and sleep behaviours.

The cluster- RCT will recruit 4 primary schools in South Lanarkshire (2 control and 2 intervention), with one class of children from each school recruited (n = 30 approx.). During prior co-design workshops, and from findings of an ongoing study, stakeholders (teachers, parents, and children) will help determine the duration of the homework tasks, their frequency, their contents, and the design of the app. Additionally, they will provide opinion on the duration of intervention however, it will be for a minimum of 8 weeks and no longer than 12 weeks. As such, the HH app will include up to 12 weeks of homework tasks to be completed by the children. Reminders to remain active for the remaining weekdays and weekend days will be included to encourage habitual health behaviours. Children will be measured at two points during this period: pre-intervention (1-week prior to intervention delivery) and post intervention (1 week after the intervention).

Measures within the cluster-RCT include demographic information, body mass, physical activity, sedentary behaviour and sleep.

Inclusion Criteria:

• children aged 8-12 years old. Hold the ability to carry out homework tasks via digital platform, mostly independently.

Exclusion Criteria:

• children outwith the age range.

For ethical and data protection reasons.

Allocation of group assignment will be concealed from the participants and primary researcher until after baseline testing with the researcher overseeing the randomisation task not involved with recruitment.