Objective Academic achievement varies according to gestational age but it is unclear whether achievement varies within ‘term’ (37–41 weeks gestation) or for ‘post-term’ births (≥42 weeks). We examined gestational age from preterm to post-term against a national minimum standard for academic achievement in population data.

Design Literacy and numeracy data of 8-year-old South Australian grade 3 children in 2008–2010 were linked to routinely collected perinatal data (N=28 155).

Results Longer gestation from 23 to 45 weeks was associated with lower risk of poor literacy and numeracy. Adjusted relative risks for being at or below national minimum standard ranged from 1.12 (95% CI 1.03 to 1.22) for ‘late preterm’ (32–36 weeks) for numeracy, to 1.84 (95% CI 1.48 to 2.30) for ‘early preterm’ (23–31 weeks) for writing. Within term, every additional week of gestational age was associated with small decreased risks of poor literacy and numeracy (eg, relative risks for poor numeracy 1.10, 95% CI 1.01 to 1.20 for 37 weeks). Population-attributable fractions for poor achievement were highest among children born ‘early term’ (37–39 weeks) due to their higher population prevalence.

Conclusions Shorter gestational age was associated with increased risk of poor literacy/numeracy. While children born ‘early term’ experience only between 1% and 10% increased risk, they constitute a larger proportion of children with poor educational achievement than preterm children, and thus are important to consider for supportive interventions to improve population-level achievement gains. The seemingly lower risk for post-term children showed large error estimates and warrants further consideration within even larger populations.