Around 80% of the world’s smokers live in lower-middle income countries and smoking rates in China, Philippines and Indonesia are very high. Evidence suggests that most people begin smoking or become habitual smokers before reaching adulthood. This highlights the need for a smoking prevention intervention focused on young people. ASSIST (A Stop Smoking In Schools Trial) is a ‘peer-led’, school-based smoking prevention intervention, shown to be effective in the UK. The aim of the study is to assess the feasibility of conducting a full-scale effectiveness evaluation of an adapted version of the ASSIST intervention in China, Indonesia or the Philippines. However, due to issues with obtaining relevant approvals, China was removed from the trial with the approval of the funder and Trial Steering Committee, and the study will only be completed in Indonesia and the Philippines.

A feasibility mixed-methods cluster randomised controlled trial in 10 schools (six intervention, four control) in each of the two countries. Participants will be students aged c13–14 in mainstream (‘lower secondary’) schools. In addition to their usual education on smoking, intervention schools will receive the ASSIST intervention which is based on ‘diffusion of innovation’ theory, with new norms and behaviours promoted through: (1) peer modelling by locally influential individuals; and (2) information disseminated by them through their social networks. Control schools will continue with their usual education around smoking prevention.

The key outcome of the study is whether prespecified progression criteria relating to recruitment, retention, acceptability and feasibility have been met in order to progress to a larger cluster randomised controlled effectiveness trial in one or more of the countries. A mixed-methods process evaluation will assess acceptability, feasibility and fidelity of intervention delivery, exposure to and reach of the intervention. The feasibility of trial processes including outcome measurement will be assessed. An economic evaluation will estimate the costs of the ASSIST intervention. Statistical analyses will focus on feasibility criteria, and qualitative data will be analysed using a framework approach. Outcomes assessed will include self-reported smoking behaviour (own and that of friends and family); vaping and other forms of nicotine use; smoking-related attitudes and knowledge; smoking norms; self-esteem; self-efficacy; (all at baseline and 7 month follow-up) and exhaled carbon monoxide concentration (at follow-up only).

The trial has been approved by the University of Glasgow College of Medical, Veterinary and Life Sciences (MVLS) Ethics Committee (ref: 200210204), the De La Salle University Research Ethics Review Committee (ref: 2023-012C) and the Medical and Health Research Ethics Committee (MHREC); Faculty of Medicine, Public Health and Nursing; Universitas Gadjah Mada (ref: KE/FK/1205/EC/2022). The trial is sponsored by the University of Glasgow (Head of Research Regulation and Compliance—debra.stuart@glasgow.ac.uk). The sponsor will not have input in data collection, management, analysis and interpretation; write up and submissions for publication.

The study findings will be disseminated through peer-reviewed publications in expert journals and conference presentations and targeted communications to schools, policymakers and the public.

ISRCTN99140476.