Background and Aims <p>Young people’s engagement in gambling can be linked to gambling-related harm. This can cause stress, anxiety, relationship issues, debt, and lost opportunities. There is a lack of independently funded, and evidence-based school-based interventions that seek to prevent and reduce the harms associated with gambling. PRoGRAM-A is one of the first independently research funded interventions to prevent gambling related harm in adolescents. This paper presents findings from an embedded process evaluation of the pilot cluster randomised control trial of PRoGRAM-A, with a specific focus on intervention fidelity, feasibility and acceptability.</p> Method <p>Multi-modal study design comprised of qualitative focus groups with students (<i>N</i> = <i>42</i>); and individual interviews with teachers (<i>N</i> = <i>7</i>), PRoGRAM-A trainers (<i>N</i> = <i>5</i>), student friends and family (<i>N</i> = <i>2</i>) and stakeholders (<i>N</i> = <i>8</i>). Structured Observations of the full cycle of PRoGRAM-A across two intervention schools were also undertaken.</p> Results <p>PRoGRAM-A was delivered with a high degree of fidelity (95%) to the training manual. It was also found to be both feasible and acceptable to students, staff and parents. It was appealing to schools as it allowed teachers to address the topic of gambling, which had already been flagged as an issue for some of the schools, but they lacked the skill and capacity to take action. Peer Supporters enjoyed the interactive nature of the training workshop. Parents and carers were supportive of the intervention and stakeholders recognised the growing need for a non-industry funded school-based intervention to raise awareness among students of gambling and gambling-related harm (GRH). Suggested intervention refinements include embedding examples of lived experience to aid students’ engagement with the topic of gambling and GRH. Increasing social skills activities to ensure students are comfortable and confident when initiating conversations and making follow-up sessions more interactive (in-line with the two-day workshop).</p> Conclusions <p>This study demonstrated that it is feasible and acceptable to deliver the PRoGRAM-A gambling harm reduction intervention within secondary schools with a high degree of fidelity. Addressing the topic of gambling and GRH within the school curriculum was deemed to be acceptable by all sample groups, including students.</p> Trial registration <p>Research Registry researchregistry8699.</p>