Co-creating School Community Intervention Program on Physical Activity to Increase Health Equity in Children and Adolescents

The goal of this observational and interventional study is to understand whether environmental and behavioral interventions can improve physical activity and health outcomes in children aged 12-16 years attending VDU Atžalynas Progymnasium, Lithuania. The main questions it aims to answer are: 1. Does higher physical activity and improved lifestyle reduce health disparities among children living in disadvantaged social and economic conditions? 2. What is the relationship between environmental pollution, physical activity, and children's health indicators? Researchers will compare data from the cross-sectional group (baseline measurements only) and the intervention group (7-day activity tracking and follow-up after 3 months) to see if targeted environmental interventions improve children's physical activity, sleep quality, and health outcomes. Participants will: * Fill in questionnaires about health behaviors, well-being, and living environment (children and parents). * Undergo physical measurements (blood pressure, height, weight, body composition). * Wear a smart wristband for 7 days to monitor activity, sleep, and heart rate (only for selected participants). * Attend a follow-up visit after 3 months (intervention group only).