Action 3:30 - Promoting increased children's physical activity through a teaching assistant-led extra-curricular programme.

All measures will be assessed at baseline (time 0), at the end of the intervention period (time 1), and 3-4 months after the intervention has ended (time 2). As the present study is a feasibility study, our primary interest is in estimating the recruitment of schools and children, adherence with the allocated intervention, and completeness of data collection for outcomes and costs.

We will record the total number of schools that were invited to take part in Action 3:30. The method of recruitment and the response rate will be documented. Information on the recruitment of TAs to the project will be provided. TAs will be asked to state their primary reason for signing-up to the project. The recruitment rates of pupils will also be recorded. The age and gender of all TA and pupil participants will be documented. Parents of children who do not want to take part will be asked to provide information on why their child decided not to participate. The TAs delivering the after-school sessions in the intervention schools will keep a register of participants at each session.

The most likely primary outcome in a future definitive trial will be accelerometer-determined minutes of MVPA per day. Accelerometers provide accurate and reliable assessments of PA among young people. Participants will wear accelerometers for five days (including two weekend days). The accelerometers will be set to record at 10 second epochs. Periods greater than an hour with zero values will be considered non-wear time and will be removed from the data. Mean minutes of MVPA will be established for weekdays and weekend days using cut-points developed for children. Accelerometer counts per minute (CPM), an indication of the volume of activity in which the children engage, will be derived. As the intervention is specifically focussed on the after-school period, we will also assess both MVPA and CPM during the after-school period (3:30pm to 8:30pm).

It is envisaged that in a future trial the primary comparison will be at time 1, with this assessment designed to assess the effect of attending the ACTION 3:30 clubs while they are still running. The time 2 assessments would be secondary comparisons designed to establish if there is a longer-term effect once the intervention sessions have ended.

As it is possible that an increase in PA after-school may reduce the opportunities to engage in screen-viewing we will assess child self-reported screen-viewing at each of the three assessment periods. We will also assess five further self-reported variables which were selected as they may function as potential mediators of behaviour change in a full trial. The five constructs are:

1. Autonomous and controlled motivation for PA. This will be measured using items adapted from the Behavioural Regulations for Exercise Questionnaire and some newly developed items.
2. Perceived PA-based autonomy, competence & relatedness need satisfaction.
3. Perceived enjoyment of PA.
4. Self-esteem, measured using the 'general' sub-scale of the Self-description Questionnaire.
5. Maternal and paternal PA support (logistic, modelling & sedentary restriction), measured using the Activity Support Scale.

Height and weight will be assessed in socks and light clothing (shoes, coats and jumpers will be removed and pockets emptied). Height will be measured to the nearest 0.1 cm using a portable SECA stadiometer. Body weight will be assessed to the nearest 0.1kg using a digital SECA scale. Body mass index (BMI = kg/m2) will be calculated and converted to an age and gender-specific BMI standard deviation score (BMI SDS). This information will be collected by Action 3:30 project staff; all staff will be trained to record height and weight according to CDC criteria by the Primary Investigator.

We are unsure of the impact that special educational needs (SEN) will have upon the recruitment and retention of children to the project. Additionally, certain disabilities may affect the collection and analysis of the accelerometry data (for example, wheelchair users). Therefore, we will record whether or not children require SEN provision in relation to physical education. This information will be collected on the parent-completed demographic information form.

Post-intervention qualitative research will be conducted with key stakeholders in some schools. Two focus groups will be conducted with participant children in five purposively-selected intervention schools to explore their opinions of the after-school element of the programme. One TA from each intervention school will be interviewed in order to consider their views of the project (the training and after-school sessions). We will also interview a member of administrative staff at five intervention and five control schools. This information will help us determine the impact Action 3:30 had on the school and identify aspects of the project that need to be improved.

Accurate assessments of the financial expenditure on the development and delivery of RCTs is of great importance to applicants and funding agencies. To provide detailed information on the feasibility of Action 3:30 we will develop a framework for an economic evaluation. All expenditure will be recorded for the various stages of the project (formative work, intervention, analysis, and dissemination). This will provide an accurate reflection of the finances required to develop, implement, and assess the intervention.