This cluster randomized trial is conducted in Beijing primary schools to evaluate the efficacy of a WeChat mini-program-based high-temperature early warning intervention on the physical and cognitive health of school-age children. Six participating schools are randomly assigned to two parallel groups. The intervention group receives tiered heat alerts and guided self-health monitoring via the mini-program. The control group follows standard daily school and family routines, with no dedicated digital high-temperature early-warning intervention. The primary outcome is children's executive function after a 2.5-month follow-up. A range of secondary indicators related to physical status, mental health and health behaviors are assessed concurrently to quantify the intervention's benefits in mitigating adverse health outcomes caused by high temperatures.