The goal of this clinical trial is to learn whether a short, teacher-delivered mental health literacy (MHL) program can help improve mental health knowledge, reduce stigma, and encourage help-seeking among preteens in Japan. Participants are students in grade 5 (age 10-11) and grade 6 (age 11-12) attending public elementary schools.

The main questions this study aims to answer are:

• Does the program increase students' knowledge about mental health and illnesses?
• Does it reduce stigma toward people with mental illnesses?
• Does it increase willingness to seek help and support peers?

Researchers will compare students who receive the program with those who follow the usual school curriculum.

Participants will:

• Answer short self-report questionnaires before, right after, and three months after the program
• Learn through a 45-minute classroom session that includes slides, a short animated film, and review activities
• Be part of regular school classes led by their homeroom teacher

The goal is to understand whether a concise and scalable MHL education can support early mental health awareness and prevention in younger youth.

The results may help schools provide effective mental health education at an early age.

This study used a cluster randomized controlled trial design, with randomization at the school level. Eight public elementary schools in Kanazawa City were assigned to either intervention or control groups using simple randomization by external staff not involved in implementation.

The intervention, the Short Mental Health Literacy Program (SMHLP), consisted of a 45-minute classroom lesson delivered by homeroom teachers. The lesson included three parts: a slide-based introduction to mental health, a 10-minute original animation about a student experiencing psychological stress, and a worksheet-based reflection activity. Teachers used self-guided materials including videos and manuals to prepare.

Primary outcome measures included an 8-item true/false knowledge scale (range: 0-8), a 5-item social distance scale (range: 5-20), and binary-response questions on help-seeking intention and willingness to support peers. The internal consistency of the knowledge scale was acceptable (Cronbach's α = 0.65), and that of the stigma scale was good (Cronbach's α = 0.88).

Data were collected at three time points: before the intervention (T1), immediately after (T2), and three months later (T3). **Statistical analyses were conducted using linear mixed models (LMM) for continuous outcomes and logistic regression mixed models (LRMM) for binary outcomes. Three-level hierarchical structures were modeled for LMM, with time nested within students and students nested within schools. School-level clustering was adopted. For LRMMs, two-level models were used without random effects for schools due to convergence issues. Intention-to-treat analyses were conducted.** Subgroup analyses were performed by grade level.

Parental opt-out consent procedures were used, and verbal assent was obtained from students. The study was approved by the University of Tokyo Human Research Ethics Committee (Approval No. 15-118).

Inclusion Criteria:

• Students enrolled in 5th or 6th grade at one of the eight participating public elementary schools in Kanazawa, Japan.
• Aged 10-12 years old.
• Passive consent obtained from guardians; verbal assent obtained from children.
• Able to complete self-report questionnaires.

Exclusion Criteria:

• Students whose parents/guardians opted out of the study.

Note: Students who were absent on the day of the pre-test (T1) were excluded from the analysis population but not from the initial study cohort.

De-identified data may be made available upon request. The final decision on data sharing will be made in consultation with the principal investigator.

Data may become available beginning 6 months following publication and up to 36 months after publication, pending approval by the principal investigator.

Access to the data may be granted to qualified researchers affiliated with academic institutions for secondary analyses. Requests will be reviewed by the research team in consultation with the principal investigator to ensure ethical and legal compliance.

Although classroom teachers may have been aware of group assignment, participants (students) were not informed of the study condition.