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How inequality shapes childen's "natural" ability from day one: an extract from The Inner Level.
Rather than innate ability determining where people end up in a supposedly meritocratic hierarchy, the apparent abilities of children and their subsequent social status are instead heavily influenced by their family's position in that hierarchy. Vast numbers of studies have now demonstrated the cognitive damage that living in poverty does to children. They also provide strong evidence that lower levels of ability among children in poorer families reflect the less stimulating and more stressful family circumstances that poverty produces. The cognitive deficits found in studies of children from poorer families show clearly that they are created, rather than being innate and unalterable givens.
A recent study in the United States used MRI scanners to scan children's brains up to seven times each between the ages of 5 months and 4 years. Comparing children from high- , medium- and low-income families, it found that children in lower-income families had lower volumes of grey matter (containing neural cells, dendrites and synapses), which is essential for cognition, information processing and behavioural regulation.
Although there were not clear ordered differences at 5 months, by 4 years of age the volume of grey matter was around 10% lower among children from less well-off families compared to the most well-off group. These differences were not accounted for by infant birth weight, early health, or by differences in head size at birth. Nor were the differences explained by maternal smoking, excessive drinking in pregnancy, birth complication, significant language or learning disorders and a number of other risk factors: children with risk factors such as these were excluded at the start of the study. Differences in brain volume between the income groups emerged and widened as children grew up and were exposed to their contrasting home environments for longer.
Other studies have also shown that the harmful effects of relative poverty on children's cognitive development become more severe when their families remain in poverty for longer periods. Data from the Millennium Cohort Study in the UK showed not only that children in poverty had lower cognitive development scores at 3, 5 and 7 years old, but that the longer they lived in poverty, the more marked the effects were. The evidence that the more time families spend in relative poverty, the worse the effects on the cognitive development of children has been clear from numerous studies for more than 20 years. Family income has been found to be a more powerful determinant of children's level of cognitive development at age 3 than either maternal depression or whether children are brought up by single parents, married or cohabiting parents.
The ways in which poverty damages development seem to be mediated by stress and lack of mental stimulation. A study that measured levels of the stress hormone cortisol in the saliva of infants of 7 months, 15 months and 2 years old, found that the cognitive deficit of poor children was closely related to their cortisol levels, indicating that the effects of poverty were transmitted by stress. In another study, researchers measured the mental stimulation children received, their parents' parenting style, the quality of the physical environment and the child's health. They found that these factors completely accounted for the effects of poverty on cognitive development. Confirming the role of stimulation, it has been shown repeatedly that if children from poor families are enrolled in parental and child support services such as Early Head Start in the US, children's performance improves and some of the effects of poverty are offset.
When parents' ability to provide a nurturing and stimulating environment for development is compromised by their experiences of inequality, then children miss out on some of the essential building blocks for development and later educational attainment. The bottom graph, left, shows that children growing up in professional families in the US hear a vastly richer vocabulary during their early years than children in working-class families or families receiving benefits.
Perhaps the most striking illustration of how educational inequalities are a consequence of socio-economic inequalities, rather than a cause, comes from a series of studies of UK children that tracks educational performance over time, comparing high and low achievers from different social backgrounds. The most recent of these studies is shown in the top graph. It compares the educational performance of children from more and less deprived backgrounds over time. Their progress is charted from their initial test results at age 7 (shown as high, average and low on the left), and, moving rightwards, tracking their subsequent performance at ages 11, 14, 16, 18 and then at university.
Regardless of whether their initial scores are high, medium or low, the gap between the performance of children from the most and the least deprived backgrounds (the gap between the continuous and the dashed lines) widens as they get older. Children from the least deprived families either maintain their initial high relative position, or improve their average or low scores. Education enhances their performance. In contrast, the relative performance of children from deprived backgrounds who initially achieved a high or average score declines over time.
Deprivation makes so much difference that children from the least deprived backgrounds whose performance at age 7 was only average or low, overtake - or at least catch up with - children who initially performed better than them but came from deprived backgrounds. And we should keep in mind that by age 7, when the top graph starts, family background has already had major effects on children's cognitive development. In summary, the chart shows that family background trumps what people continue to regard as ``natural'' ability in accounting for children's educational performance over time.
An OECD study of resilience showed that in some countries, up to 70% of poor children are educationally resilient, whereas in the UK, less than a quarter of children manage to exceed expectations based on family socioeconomic circumstances. It is clear that differences in cognitive development and intelligence are the consequence of inequality rather than its cause.
• Extracted from The Inner Level: How More Equal Societies Reduce Stress, Restore Sanity and Improve Everyone's Wellbeing by Richard Wilkinson and Kate Pickett.