OBJECTIVE:To examine the individual and collective contribution of biological and socioenvironmental factors associated with language function at 2, 5, 7, and 13 years in children born preterm (<30 weeks' gestation or <1250 g birth weight). METHODS:Language function was assessed as part of a prospective longitudinal study of 224 children born preterm at 2, 5, 7, and 13 years using age-appropriate tools. Language Z-scores were generated based on a contemporaneous term-born control group. A selection of biological factors (sex, small for gestational age, bronchopulmonary dysplasia, infection, and qualitatively defined brain injury) and early socioenvironmental factors at age 2 years (primary income earner employment status and type, primary caregiver education level, English as a second language, parental mental health history, parent sensitivity and facilitation, and parent-child synchrony) was chosen a priori. Associations were assessed using univariable and multivariable linear regression models applied to outcomes at each time point. RESULTS:Higher primary caregiver education level, greater parent-child synchrony, and parent sensitivity were independently associated with better language function across childhood. Socioenvironmental factors together explained an increasing percentage of the variance (9%-18%) in language function from 2 to 13 years of age. In comparison, there was little evidence for associations between biological factors and language function, even during early childhood years. CONCLUSION:This study highlights the importance of socioenvironmental factors over biological factors for language development throughout childhood. Some of these socioenvironmental factors are potentially modifiable, and parent-based interventions addressing parenting practices and education may benefit preterm children's language development.