A cluster randomized trial of a combined Mental Health Literacy (MHL) and Dialectical Behavior Therapy (DBT) classroom-based intervention.

A pan-Canadian cluster randomized trial (by classroom) was conducted to examine the effects of a combined mental health literacy and dialectical behavior therapy skills program implemented by teachers on protective factors related to social and emotional well-being, including mindfulness, emotion regulation, inclusive education, distress tolerance, mental health knowledge, reduction of stigma, and help-seeking skills. The sample of 111 classrooms drawn from three urban centers and 67 schools, which were randomly assigned to intervention or control, included 1,750 students in third- to 12th-grade classrooms. Student-reported measures of mindfulness, emotion regulation, inclusive education, distress tolerance, mental health literacy, and classroom climate were collected three times in the year (October, February, and June). Teachers recorded dosage and fidelity data, and in-class observations took place to support implementation data. Results indicated the intervention classrooms demonstrated statistically significant improvements relative to the changes in the control classrooms on six of eight dependent variables: mindfulness, emotion regulation, impulse control, strategies, beliefs about mental illness, and stigma. Effect sizes were large for mindfulness, medium for emotion regulation and stigma, and small for impulse control and beliefs about mental illness. There was no evidence that intervention effects were moderated by intervention site, school level, or student characteristics related to Indigenous heritage, gender, or whether students received English language learner services. By contrast, the mid- to postintervention effect on mindfulness differed for students receiving special education services, such that effects were greater for students receiving special education services compared to students not receiving special education services. (PsycInfo Database Record (c) 2026 APA, all rights reserved).