An informal school-based peer-led intervention for smoking prevention in adolescence (ASSIST): a cluster randomised trial

Background Schools in many countries undertake programmes for smoking prevention, but systematic reviews have shown mixed evidence of their effectiveness. Most peer-led approaches have been classroom-based, and rigorous assessments are scarce. We assessed the effectiveness of a peer-led intervention that aimed to prevent smoking uptake in secondary schools. Methods We undertook a cluster randomised controlled trial of 10 730 students aged 12–13 years in 59 schools in England and Wales. 29 schools (5372 students) were randomly assigned by stratified block randomisation to the control group to continue their usual smoking education and 30 (5358 students) to the intervention group. The intervention (ASSIST [A Stop Smoking In Schools Trial] programme) consisted of training influential students to act as peer supporters during informal interactions outside the classroom to encourage their peers not to smoke. Follow-up was immediately after the intervention and at 1 and 2 years. Primary outcomes were smoking in the past week in both the school year group and in a group at high risk of regular smoking uptake, which was identified at baseline as occasional, experimental, or ex-smokers. Analysis was by intention to treat. This study is registered, number ISRCTN55572965. Findings The odds ratio of being a smoker in intervention compared with control schools was 0·75 (95% CI 0·55–1·01) immediately after the intervention (n=9349 students), 0·77 (0·59–0·99) at 1-year follow-up (n=9147), and 0·85 (0·72–1·01) at 2-year follow-up (n=8756). The corresponding odds ratios for the high-risk group were 0·79 (0·55–1·13 [n=3561]), 0·75 (0·56–0·99 [n=3483]), and 0·85 (0·70–1·02 [n=3294]), respectively. In a three-tier multilevel model with data from all three follow-ups, the odds of being a smoker in intervention compared with control schools was 0·78 (0·64–0·96). Interpretation The results suggest that, if implemented on a population basis, the ASSIST intervention could lead to a reduction in adolescent smoking prevalence of public-health importance.