Phase 1 MASTER Coach Development Workshop (weeks 1) PE teachers participated in a 6-hour theory and practical teacher education workshop via Zoom to a member of the research team (JY), including four hours of reading relevant papers and books regarding the game-based approach (GBA) (Game-sense, Invasion Games, Small-sided games and tactical approach). The latest evidence regarding sport, coaching and youth was presented, and the MASTER framework was explained. A combination of lectures, discussions and group work activities provided coaches with the theoretical underpinnings and practical applications of the MASTER elements. It allowed coaches to plan and assess sessions based on the MASTER framework and evaluation tool. A key target for the workshop was to empower coaches with the necessary skills and understanding to use the MASTER framework when designing new training activities or adapting existing activities. Coaches were provided with a PowerPoint presentation, printed course booklet, MASTER checklist, and printed (and explained) examples of basketball training activities and planning tasks. The workshop components (e.g., PowerPoint presentations, workshop materials, practical sessions) were designed and developed to minimise the impact of the presenters' biographies on knowledge uptake and ensure suitability for future scale-up (whereby external presenters would deliver the MASTER program).

Phase 2 Eight weeks of teaching mentoring (weeks 2-7) This 8-week phase involved coaches implementing MASTER elements (e.g. 10-minute stretching before a sports game, teachers will give 1-2 sentences of praise during the game for individual students who make a reasonable effort) in their regular training sessions (2 x 1 ½ hour sessions per week) under the guidance of the coach mentor (2-3 experienced coaches who from the member of the research team will evaluate the mentor). The mentor spent one session per week (1 ½ hour) for eight weeks, rotating between coaches to assist in applying the MASTER framework and providing ongoing support. This included access to a discussion platform on Facebook messenger, providing example session activities and MASTER learning activities via the purpose-designed MASTER website, and feedback on draft session plans. During and after the training sessions, the mentor also stimulated dialogue and provided input to coaches regarding potential ways to increase the engagement of players (e.g., adaption of the session activities), questioning techniques to facilitate player reflection and learning, session evaluation and coach reflection; identification of the elements of MASTER in action; and identification of the potential missed opportunity to include an element of MASTER.

Phase 3 3 weeks peer peer-assessed teaching/discussions (weeks 8-10) The mentor prepared and implemented a 2-hour training session highlighting important aspects of the MASTER framework and games-based coaching practices. Coaches were involved in evaluating the mentor using the MASTER observation checklist, and a group discussion based on the checklist and coach observations facilitated the learning episode. This collaborative practise incorporates what is known about professional learning communities and instructional "rounds", and is now common in higher educational settings. The literature supports that learning and understanding are optimised when learners are involved in the feedback process, explicitly learn to become assessors, have a clear framework to evaluate performance, and provide feedback through a discussion or dialogue. Following the coach assessment and reflection session, coaches continued implementing MASTER strategies in their regular training sessions. They were required to undertake a peer observation of a colleague alongside the coach mentor (using the MASTER observation checklist). Feedback and professional dialogue followed the peer observation sessions. Peer dialogue has shown to be an effective and well-received method for improving coaching practices.

Frequency: Participated teachers will be asked to participate in Weekly 2-3 hour game sessions in school, which is an additional component of the intervention (with the teacher's regular class). The sessions will be facilitated by the teacher and supervised by a study team member (weekly 30-40-minute telephone calls with members of the research team discussing strategies for improving game sessions).