Study objective: The aim of this study was to determine the effect of a multilevel school based intervention on adolescents' emotional wellbeing and health risk behaviours.
Design: School based cluster randomised controlled trial. Students were surveyed using laptop computers, twice in the first year of intervention and annually thereafter for a further two years.
Setting: Secondary schools.
Participants: 2678 year 8 students (74%) participated in the first wave of data collection. Attrition across the waves was less than 3%, 8%, and 10% respectively with no differential response rate between intervention and control groups at the subsequent waves (98% v 96%; 92% v 92%, and 90% v 89% respectively).
Main results: A comparatively consistent 3% to 5% risk difference was found between intervention and control students for any drinking, any and regular smoking, and friends' alcohol and tobacco use across the three waves of follow up. The largest effect was a reduction in the reporting of regular smoking by those in the intervention group (OR 0.57, 0.62, and 0.72 at waves 2, 3, and 4 respectively). There was no significant effect of the intervention on depressive symptoms, and social and school relationships.
Conclusions: While further research is required to determine fully the processes of change, this study shows that a focus on general cognitive skills and positive changes to the social environment of the school can have a substantial impact on important health risk behaviours.