BACKGROUND: Recent data suggest that children of mothers who are obese before pregnancy, or who gain too much weight during pregnancy, may be at an increased risk of cognitive impairments. METHODS: Mother–infant dyads enrolled in a birth cohort study in Pittsburgh, Pennsylvania (1983–1986), were followed from early pregnancy to 14 years postpartum (n=574). Math, reading and spelling achievements were assessed at ages 6 and 10 years using the Wide Range Achievement Test-Revised, and at age 14 years using the Wechsler Individual Achievement Test Screener. Self-reported total GWG was converted to gestational age-standardised z-scores. Generalised estimating equations were used to estimate the effects of GWG and pre-pregnancy body mass index (BMI) on academic achievement at 6, 10 and 14 years, while adjusting for maternal race, child sex, parity, employment, family income, maternal intelligence, maternal depression, pre-pregnancy BMI (in GWG models only) and the home environment. RESULTS: The mean (SD) BMI was 23.4 (5.7) kg/m and the mean (SD) GWG reported at delivery was 14.4 (5.9) kg. There was a significant non-linear association between pre-pregnancy BMI and an offspringʼs academic achievement. At 6, 10 and 14 years, an offspringʼs academic scores were inversely associated with pre-pregnancy BMI beyond 22 kg/m. High GWG (>1 SD) was associated with approximately 4-point lower reading (adjusted β (adjβ) −3.75, 95% CI −7.1 to −0.4) and spelling scores (adjβ −3.90, 95% CI −7.8 to −0.2), compared with GWG −1 to +1 SD. CONCLUSIONS: Future studies in larger and socioeconomically diverse populations are needed to confirm maternal weight and weight gain as causal determinants of a childʼs academic skills, and whether this effect persists into adulthood.