Unequal educational outcomes for children with similar early childhood vocabulary but different socio-economic circumstances

In 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). We ran preregistered analyses of the nationally-representative UK Millennium Cohort Study data (N=15,576), sharing all analysis code and data definitions to support follow-up and reproducibility. We show that age-5 vocabulary strongly predicted age-16 educational attainment even after adjusting for both SEC and caregiver vocabulary ability. However, the weight of evidence for the effect was lower than that for the effect of SEC. Further, larger vocabulary was most advantageous for those in middle SEC groups. This demonstrates the current limits of meritocracy in education attainment. It suggests that early language interventions are well founded but cannot by themselves be expected to counteract the effect of social inequality on life chances.