["Journal of Child Psychology and Psychiatry, EarlyView. ", "\n\nBackground\nIn a purely meritocratic society, educational outcomes would reflect ability and only ability. Vocabulary size is a common measure of cognitive ability that predicts educational outcomes but is confounded with socioeconomic circumstances (SEC).\n\n\nMethods\nIn preregistered analyses of the nationally representative UK Millennium Cohort Study data (N = 15,576), we used a series of multiple linear and logistic regression analyses to investigate the predictive value of age‐5 vocabulary for age‐16 educational outcomes and assess whether socioeconomic circumstance moderated this relation.\n\n\nResults\nWe show that age‐5 vocabulary strongly predicted age‐16 educational attainment, even after adjusting for both SEC and caregiver vocabulary (OR = 1.62, 95% CIs = [1.52; 1.72]; β = .22, 95% CIs = [0.19; 0.24]). SEC also predicts educational attainment (OR = 2.05, 95% CIs = [1.92; 2.19]), and modifies the association between vocabulary and educational attainment, whereby a larger vocabulary was most advantageous for those in middle SEC groups (interaction term OR = 1.09 [1.03; 1.15]).\n\n\nConclusions\nEarly child vocabulary is a strong predictor of children's educational outcomes – even when controlling for proxy measures of the home environment and genetics. Nonetheless, children who enter school with strong vocabulary skills but disadvantaged socioeconomic circumstances still have only about a 50/50 chance of gaining gateway qualifications at age 16.\n\n"]