BACKGROUND: Preterm birth and childhood poverty each adversely impact children’s cognitive development and academic outcomes. In this study, we investigated whether the relationships between preterm and early term birth and children’s cognitive scores at 3, 5, and 7 years old were modified by childhood poverty. METHODS: This study was conducted by using data on singletons born at 24 to 40 weeks’ gestation enrolled in the Millennium Cohort Study in the United Kingdom. Linear regression models were used to test independent and joint associations of gestational age (early or moderate preterm, late preterm, or early term compared with term) and childhood poverty (<60% of median UK income) with children’s cognitive scores. Presence of additive interaction between gestational age and poverty was tested by using interaction terms. RESULTS: Children born preterm (<37 weeks) or early term (37–38 weeks) tended to score more poorly on cognitive assessments than children born at term (39–40 weeks). The estimated deficits were ∼0.2 to 0.3 SD for early or moderate preterm, 0.1 SD for late preterm, and 0.05 SD for early term compared with term. Children living in poverty scored 0.3 to 0.4 SD worse than children not living in poverty on all assessments. For most assessments, the estimated effects of the 2 factors were approximately additive, with little or no evidence of interaction between gestational age and poverty. CONCLUSIONS: Although children born preterm who lived in poverty had the poorest cognitive outcomes, living in poverty did not magnify the adverse effect of being preterm on cognitive development.