AbstractBackgroundGestational age is positively associated with cognitive development, but socio‐demographic factors also influence school performance. Previous studies suggested possible interaction, putting children with low socio‐economic status (SES) at increased risk of the negative effects of prematurity.ObjectivesTo investigate the association between gestational age in weeks, socio‐demographic characteristics, and school performance at the age of 12 years among children in regular primary education.MethodsPopulation‐based cohort study among liveborn singletons (N = 860,332) born in the Netherlands in 1999–2006 at 25–42 weeks' gestation, with school performance from 2011 to 2019. Regression analyses were conducted investigating the association of gestational age and sociodemographic factors with school performance and possible interaction.ResultsSchool performance increased with gestational age up to 40 weeks. This pattern was evident across socio‐demographic strata. Children born at 25 weeks had −0.57 SD (95% confidence interval −0.79, −0.35) lower school performance z‐scores and lower secondary school level compared to 40 weeks. Low maternal education, low maternal age, and non‐European origin were strongly associated with lower school performance. Being born third or later and low socioeconomic status (SES) were also associated with lower school performance, but differences were smaller than among other factors. When born preterm, children from mothers with low education level, low or high age, low SES or children born third or later were at higher risk for lower school performance compared to children of mothers with intermediate education level, aged 25–29 years, with intermediate SES or first borns (evidence of interaction).ConclusionsHigher gestational age is associated with better school performance at the age of 12 years along the entire spectrum of gestational age, beyond the cut‐off of preterm birth and across socio‐demographic differences. Children in socially or economically disadvantaged situations might be more vulnerable to the negative impact of preterm birth. Other important factors in school performance are maternal education, maternal age, ethnicity, birth order and SES. Results should be interpreted with caution due to differential loss to follow‐up.