Abstract
BACKGROUND: A majority of adolescents do not meet the recommended levels of physical activity, while reported levels of mental health problems are increasing, and socioeconomic disparities in academic performance are widening. Many schools are implementing physical activity in different forms, but there is inconclusive evidence on what types of interventions improve mental health, cognitive functions, and academic performance and how to implement such interventions. There is a critical need for integrated, feasible, and equitable interventions. The objective of this study is to develop an effective multi-component school-based intervention that will target both physical activity and homework support during an extended school day and evaluate its effects on mental health, cognitive function and academic performance. METHODS: The study is designed as a cluster-randomised controlled trial with 54 schools and approximately 2,700 students in grade 8 (age 14-15). The intervention includes three weekly 60-minute sessions: (1) Different types of physical activities (2), Homework support with short activity breaks, and (3) Walking and listening to audiobooks. This study will evaluate both outcome effects and implementation process. The primary outcome is anxiety, assessed using the Spence Children's Anxiety Scale (SCAS-S). Secondary outcomes include physical activity, sedentary time and behaviours measured by accelerometry and questionnaire, cognitive functions assessed by a computer-based test battery, mental health and sleep with questionnaires, and academic performance by grades. Process evaluation will include fidelity, dose, feasibility, acceptability and context, using structured documentation, interviews, focus groups, and observations. The effectiveness of outcomes between groups will be assessed using mixed-effects regression analysis, adjusting for relevant covariates. Process data will be analysed using descriptive statistics and content, and thematic analysis. DISCUSSION: This study addresses key knowledge gaps in school-based health promotion by integrating physical activity and homework support within the school structure. The results will yield insights into both effectiveness and implementation, informing future policy and practice in schools to promote health and facilitate students' learning. The intervention targets youth in diverse socioeconomic contexts and is expected to contribute to reducing health and education inequalities. TRIAL REGISTRATION: The trial was retrospectively registered on April 27, 2021. ISRCTN78666212.