This study compared healthy late-preterm (34-36 week) and healthy full-term (37-41 week) singleton infants on a range of cognitive, motor, and behavioral outcomes at 2 and 4 years. Eighteen developmental outcomes were analyzed using the Early Childhood Longitudinal Survey-Birth Cohort, a nationally representative panel study. Ordinary Least Squares and logistic regressions were performed to estimate unadjusted and adjusted differences in developmental outcomes between late-preterm and full-term children. In unadjusted models, late-preterm children scored more poorly than full-term children on most assessments of cognitive ability at 2 and 4 years. After adjusting for demographic, economic, and obstetrical factors, late-preterm children continued to score lower than full-term children on language use at 2 years and on literacy, language, and math at 4 years, but scored at least one standard deviation below the mean on only one of the eighteen outcomes. Late-preterm birth is associated with subtle deficits in cognitive functioning as early as age 2 years. Although the effects may be too small to have clinical relevance, they suggest a trend toward poorer outcomes that have been documented at older ages and suggest that early testing and intervention may enhance the cognitive development of late-preterm children.