Mindfulness in the school curriculum? A nationwide cluster-randomized trial of the effectiveness of implementing a mindfulness-based intervention for 9–16-year-olds students in Danish elementary schools

This study aimed to investigate the effectiveness of a teacher-training program for integrating a ten-session, school-based mindfulness program into regular classroom instruction in Danish elementary schools. The focus was on the mental health of students in grades 4 to 9. The primary study population comprised at-risk students, with the total students serving as a secondary study population. We also examined whether intervention effects were modified by sex and grade.

In a nationwide cluster-randomized trial in 2019–2020 (during COVID-19), schools were randomized 1:1 to either the intervention (54 schools, 97 teachers, 836 students, including 186 at-risk students) or teaching as usual (56 schools, 94 teachers, 892 students, including 165 at-risk students). Thirteen validated self-report measures of mental health were collected at baseline, five, and eight months, with the Strengths and Difficulties Questionnaire Total Difficulties Score as the primary outcome. Intention-to-treat analyses were performed using mixed-effects linear regression models and bootstrapping.

Follow-up data were obtained from 25 intervention schools (605 students, including 129 at-risk) and 28 teaching-as-usual schools (745 students, including 143 at-risk). Among at-risk students, Cohen's d for the Total Difficulties score at eight months was 0.05 (95 % CI -0.29 to 0.40), and no statistically significant effect was observed in the total study population.

Secondary analyses indicated that the intervention led to increased perceived hyperactivity/inattention—particularly among boys and younger students—and poorer self-rated health among at-risk students.

A deeper understanding of the mechanisms in school-based mindfulness-based interventionss and key factors for implementing them with fidelity requires further investigation.