This study used a short-term longitudinal design to examine the role of effortful control, behavior problems, and peer relations in the academic adjustment of 74 kindergarten children from primarily low-income families. Teachers completed standardized measures of children's effortful control, internalizing and externalizing problems, school readiness, and academic skills. Children participated in a sociometric interview to assess peer relations. Research Findings: Correlational analyses indicate that children's effortful control, behavior problems in school, and peer relations are associated with academic adjustment variables at the end of the school year, including school readiness, reading skills, and math skills. Results of regression analyses indicate that household income and children's effortful control primarily account for variation in children's academic adjustment. The associations between children's effortful control and academic adjustment do not vary across the sex of the child or ethnicity. Mediational analyses indicate an indirect effect of effortful control on school readiness through children's internalizing problems. Practice or Policy: Effortful control emerged as a strong predictor of academic adjustment among kindergarten children from low-income families. Strategies for enhancing effortful control and school readiness among low-income children are discussed.