Young children born preterm may be more affected by environmental influences than their full-term peers. Few studies have investigated whether such effects exist for older children and young adolescents. With participants aged 9 and 13 years, we examine whether children born preterm could be differentially affected by the quality of their relationship with their mothers and fathers. We used the Growing Up in Ireland dataset: a longitudinal sample of 8,568 children in Ireland (51.4% female, 48.6% male) and their parents. We found that parent--child conflict was consistently associated with poorer verbal, numerical, and socioemotional outcomes; in some instances, parent--child closeness was associated with better outcomes. Being born very preterm was consistently associated with negative outcomes. We found support for a diathesis-stress model of preterm birth in just one instance: children born very preterm displayed a stronger relationship between maternal conflict and increased socioemotional difficulties.