The socio-economic gradient of cognitive test scores: evidence from two cohorts of Irish children

There is a well-established socio-economic gradient in child cognitive test scores. This gradient emerges at early ages, with some evidence that it can widen as children age. We investigate this phenomenon with two longitudinal cohorts of Irish children who take such tests at ages ranging from 9 months to 17 years, using maternal education and equivalised income as our measure of socio-economic resources. The gradient is observed from the age of 3 with tentative evidence that it widens as children get older. We have evidence on a wide range of tests and there is some evidence that the gradient is slightly stronger for tests involving crystalised as opposed to fluid intelligence. Exploiting the longitudinal nature of the data, we also investigate mobility across the distribution of test scores, with some evidence that such mobility is less among poorer children, which raises the disturbing possibility that such children could become trapped in low achievement.