Each year, 15 million babies worldwide are born preterm. Preterm birth is associated with adverse neurodevelopmental outcomes across the life span. Recent registry-based studies suggest that preterm birth is associated with decreased wealth in adulthood, but the mediating mechanisms are unknown. This study investigated whether the relationship between preterm birth and low adult wealth is mediated by poor academic abilities and educational qualifications. Participants were members of two British population-based birth cohorts born in 1958 and 1970, respectively. Results showed that preterm birth was associated with decreased wealth at 42 years of age. This association was mediated by decreased intelligence, reading, and, in particular, mathematics attainment in middle childhood, as well as decreased educational qualifications in young adulthood. Findings were similar in both cohorts, which suggests that these mechanisms may be time invariant. Special educational support in childhood may prevent preterm children from becoming less wealthy as adults.