Increasing physical activity among children in China remains a pressing concern. We designed a 16-week school-based program aimed at changing behaviors, drawing on the Behavior Change Wheel and the Theoretical Domains Framework. Subsequently, a cluster feasibility non-randomized controlled trial (RCT) was carried out with children in Yangzhou, China. This qualitative process evaluation, conducted alongside the cluster feasibility non-RCT, sought to: (1) understand how participants and providers experienced the intervention and trial; and (2) develop recommendations to guide a future, larger cluster RCT. Semi-structured interviews were conducted with 20 children (10 in the intervention group, 10 in the control), 20 parents, and 2 health education staff across two public schools in Yangzhou. All interviews were audio-recorded, fully transcribed, and translated from Mandarin into English. Thematic analysis was applied to identify patterns in the data. Analysis revealed eight main themes reflecting participant experiences: (1) strong perception of intervention components as effective in promoting activity, (2) appreciation of the program’s design, (3) factors supporting or hindering attendance and delivery, (4) positive emotions experienced during data collection, (5) satisfaction with trial management, (6) effects of personal beliefs and emotional reactions, (7) influence of social relationships on decision-making, and (8) key recruitment challenges. The program and trial procedures were generally acceptable to children, parents, and providers. School-based behavior interventions appear promising for enhancing physical activity among children aged 10–12 in China. Future cluster RCTs should address obstacles to participation and implementation to better evaluate effectiveness.
