School-based intervention to improve mental health, cognitive function, and academic performance in adolescents: a study protocol for a cluster randomised trial.

The trial is designed as a cluster-randomised controlled trial involving 54 schools and approximately 2,700 students in grade 8 (age 14-15).

• The study uses a cluster-randomised controlled trial design.
• 54 schools are included in the trial.
• Approximately 2,700 students in grade 8 (age 14-15) are the target population.
• The trial was retrospectively registered on April 27, 2021 (ISRCTN78666212).

The intervention consists of three weekly 60-minute sessions targeting physical activity and homework support during an extended school day.

• Session 1 involves different types of physical activities.
• Session 2 involves homework support with short activity breaks.
• Session 3 involves walking and listening to audiobooks.
• Each session is 60 minutes in duration and delivered three times per week.
• The intervention is designed to be integrated within the school structure during an extended school day.

The primary outcome of the trial is anxiety, assessed using the Spence Children's Anxiety Scale (SCAS-S).

• The Spence Children's Anxiety Scale (SCAS-S) is the instrument used to measure the primary outcome.
• Anxiety was selected as the primary outcome in the context of increasing reported levels of mental health problems among adolescents.

Secondary outcomes include physical activity, sedentary behaviour, cognitive functions, mental health, sleep, and academic performance.

• Physical activity and sedentary time are measured by both accelerometry and questionnaire.
• Cognitive functions are assessed by a computer-based test battery.
• Mental health and sleep are measured with questionnaires.
• Academic performance is assessed by grades.

The study includes a process evaluation assessing fidelity, dose, feasibility, acceptability, and context using multiple data collection methods.

• Process evaluation methods include structured documentation, interviews, focus groups, and observations.
• Process data will be analysed using descriptive statistics and content and thematic analysis.
• The process evaluation is designed to yield insights into both effectiveness and implementation.

Statistical analysis of outcome effectiveness between groups will use mixed-effects regression analysis adjusting for relevant covariates.

• Mixed-effects regression analysis is the planned primary statistical approach.
• Analysis will adjust for relevant covariates.
• Both outcome effects and implementation process will be evaluated.

The study was motivated by the fact that a majority of adolescents do not meet recommended physical activity levels, mental health problems are increasing, and socioeconomic disparities in academic performance are widening.

• Reported levels of mental health problems among adolescents are described as increasing.
• Socioeconomic disparities in academic performance are described as widening.
• The intervention targets youth in diverse socioeconomic contexts and is expected to contribute to reducing health and education inequalities.
• Evidence on what types of school-based interventions improve mental health, cognitive functions, and academic performance is described as 'inconclusive.'