Vitamin D is an essential micronutrient involved in calcium and phosphorus metabolism, skeletal development, immune regulation, muscle function, and several cellular processes important during childhood and adolescence. School-going children represent a particularly important population for maintaining adequate vitamin D status because this period is characterized by rapid growth, increasing skeletal mineralization, physical activity, and exposure to infectious diseases. Vitamin D insufficiency and deficiency are common among children worldwide and may result from inadequate dietary intake, limited sunlight exposure, increased adiposity, rapid growth, skin pigmentation, and lifestyle factors. The effectiveness of vitamin D supplementation in improving health outcomes among school-going children has been investigated in randomized controlled trials and systematic reviews, although findings vary according to baseline vitamin D status, dosage, duration, season, and health outcome assessed. Recent evidence indicates that supplementation is effective in increasing serum 25-hydroxyvitamin D [25(OH)D] concentrations and may provide benefits for respiratory health, particularly during periods of low vitamin D status or limited ultraviolet-B exposure. A 2025 randomized trial among 6–8-year-old children reported fewer acute respiratory tract infection-related sick days following daily vitamin D supplementation, whereas a large three-year trial among South African schoolchildren found substantial improvement in vitamin D status but no significant effects on growth, body composition, pubertal development, or spirometric outcomes. Similarly, recent evidence suggests that supplementation does not necessarily improve bone mineral outcomes in otherwise healthy children when baseline vitamin D status is adequate. Therefore, vitamin D supplementation appears most beneficial when used to prevent or correct deficiency rather than as a universal intervention for improving all aspects of child health. Future research should focus on population-specific supplementation strategies, baseline vitamin D status, optimal dosing, long-term health outcomes, and children at particularly high risk of deficiency.