Investigating how vocabulary relates to different dimensions of family socio-economic circumstance across developmental and historical time

For decades, studies have reported social inequalities in child language ability and policy makers have sought interventions to address them. Yet inequalities persist. To make better targeted progress, we need to determine precisely which aspects of Socio-Economic Circumstances (SEC - caregiver education, household income, wealth, occupational status or neighbourhood deprivation) best predict language ability and whether this is stable over developmental and historical time. We addressed these questions using large, nationally representative longitudinal datasets for two generations born 30 years apart. Substantial individual differences in child and adolescent vocabulary are explained by multiple indicators each making a unique contribution, most notably caregiver education, income and occupational status. Each step up in these measures predicts a concomitant step up in vocabulary. While inequalities are generally stable over developmental and historical time, contemporary data suggests a need to focus on widening inequalities both at the start and the end of formal schooling.