Background: Malaria surveillance and interventions in endemic countries often target young children at highest risk of malaria morbidity and mortality. School-age children and adults not captured in surveillance may contribute to malaria transmission. Methods: Cross-sectional surveys were conducted in one rainy and one dry season in southern Malawi. Demographic and health information was collected for all household members. Blood samples were obtained from individuals aged greater than six months for microscopic and PCR identification of Plasmodium falciparum. Results: Specimens were collected from 5,796 individuals. PCR prevalence of malaria infection was 5%, 10%, and 20% in dry, and 9%, 15%, and 32% in rainy seasons in Blantyre, Thyolo, and Chikhwawa, respectively. Over 88% of those infected were asymptomatic. Participants aged 6-15 years were at higher risk of infection (OR = 4.8; 95% CI, 4.0-5.8) and asymptomatic infection (OR = 4.2; 95% CI, 2.7-6.6) than younger children in all settings. School-age children used bednets less frequently than other age groups. Compared to young children, school-age children were brought less often for treatment and more often to unreliable treatment sources. Conclusions: School-age children represent an underappreciated reservoir of malaria infection and have limited exposure to antimalarial interventions. Malaria control and elimination strategies may need to expand to include this age group.