The World Health Organization (WHO) defines school-age children and adolescents (SACAs) as those individuals aged between 5 and 19 years. Despite this, the age range varies by country according to their educational system. Approximately 90% of SACAs live in low- and middle-income countries (LMICs), particularly in Africa, Asia and Latin America, constituting up to 50% of the population. The SACA period represents an important timeline in the life-course, characterised by numerous fundamental milestones in growth and development, presenting a vital opportunity for shaping future health. Across the life-course, the nutritional requirements and health challenges vary according to a wide range of individual, social/community and environmental factors shaping the health outcomes of SACAs. Informed by the WHO’s Social Determinants of Health (SDH) framework, this chapter critically explores the determinants of SACAs’ health and nutrition. The determinants of health and nutritional status among these vulnerable groups include socio-demographic and economic factors such as age, gender and household income status, family dynamics, household food security, family food choices and the food environment. There is also growing evidence that school environment, media and food advertisements and marketing influence children’s dietary preferences and consumption patterns, thereby affecting health and nutrition outcomes.