School-based mindfulness training in early adolescence: what works, for whom, and how in the MYRIAD Trial?

Abstract

Background: Preventing mental health problems in early adolescence is a priority. Schoolbased mindfulness training (SBMT) is an approach with mixed evidence. Objective: To explore for whom SBMT does/does not work and what influences outcomes. Methods: The MYRIAD was a parallel group, cluster randomised controlled trial (K=84 secondary schools; N=8,376 students, age: 11-13), recruiting schools that provided standard social-emotional learning. Schools were randomised 1:1 to continue this provision (control/teaching as usual (TAU)), and/or to offer SBMT (“.b” (intervention)). Risk for depression, social-emotional-behavioural functioning, and well-being were measured at baseline, pre-intervention, post-intervention, and 1-year follow-up. Hypothesized moderators, implementation factors, and mediators, were analysed using mixed effects linear regressions, instrumental variable methods, and path analysis. Findings: SBMT vs TAU resulted in worse scores on risk for depression and well-being in students at risk of mental health problems both at post-intervention and 1-year follow-up, but differences were small and not clinically relevant. Higher dose and reach were associated with worse social-emotional-behavioural functioning at post-intervention. No implementation factors were associated with outcomes at 1-year follow-up. Pre−post gains in mindfulness skills and executive function predicted better outcomes at 1-year follow-up, but the SBMT was unsuccessful to teach these skills with clinical relevance. Discussion: SBMT as delivered in this trial is not indicated as a universal intervention. Moreover, it may be contraindicated for students with existing/emerging mental health symptoms. Clinical implications: Universal SBMT is not recommended in this format in early adolescence. Future research should explore social-emotional learning programmes adapted to the unique needs of young people.