Predicting children’s “potential”: science or alchemy?

by Terry Wrigley, Visiting Professor, Northumbria University

Victorian politicians were untroubled by the fact that children largely entered an occupation and class position similar to their parents. In fact, it was intended that this should happen, and the school system was designed to make sure it did.

It was only in the 20th Century that such blatant talk about “educating children for their station in life” ceased to be acceptable. Then along came the theory of genetically fixed intelligence to fill a gap.

Its English pioneer Cyril Burt, London’s first educational psychologist, piloted ‘intelligence tests’ in Oxford. As might be expected, the children of university professors scored far higher than manual workers’ children. Burt jumped to the conclusion that the difference must be due to genetically inherited intelligence.

Such tests were used for the next 50 years as a gatekeeper to secondary education. The vast majority of working-class children did not score high enough for a free place in a grammar school, so remained at elementary school till leaving school at 14.

Burt later backed up his argument with studies of identical twins who had been separated by adoption. He reported a high correlation between the separated twins’ IQ scores but not with those of the adoptive parents. It was only after his death that the research turned out to be fiction – it had never actually happened.

Periodically attempts are made to repeat twins studies. The main US study selects its sample by inviting separated but reunited twins to come forward because they feel so much alike – a biased sample if ever there was one. Over half the twins in the Swedish study were only separated in the sense that one had been cared for by their mother’s sister or mother. They grew up in the same neighbourhood, went to the same school and saw each other every day.

The return of genetic intelligence

One of the statisticians from the US study, Robert Plomin, now working in London, has attempted to sidestep the problem of separation by comparing the Plomin GCSE. His logic is that all twins share the same environmental influences but only identical (monozygotic) twins share the same genes as well. By performing a simple calculation on their GCSE results, he claims to have proved that heritability accounts for 55% of everybody’s GCSE performance in maths, for example.

This seems to provide a strong argument that children’s academic potential is largely predetermined. It is underpinned by his report of a correlation of 0.83 between the GCSE maths grades of identical girl twins, 0.80 for identical boy twins.

This appears convincing until you ask what this means in practice. It is fairly straightforward to devise hypothetical models to find out, using DfE points scores for each grade. For starters, what level of correlation would result if the grades for one twin of each pair were distributed as nationally (i.e. 7% getting A*, 13% A, etc) but the second twin gets a grade higher or lower. In fact this produces a correlation coefficient of 0.82, almost identical to Plomin’s figure.

In other words, an average one-grade difference in GCSE maths even for twins with identical genes and extremely similar upbringing (home, school, youth culture and so on)! Perhaps children’s ‘potential’ attainment is not so predetermined after all.

“Intelligence” and “potential”

We often casually use the word ‘intelligence’ as if it were some kind of substance which could be measured. It is interesting that Cyril Burt used the word ‘capacity’, which harks back to attempts to determine people’s intelligence by the size of the cranium.

Similarly, we often speak about a child’s ‘potential’ as if this were something fixed. What we achieve owes as much to the culture we grow up in and the opportunities provided by our environment as to mental ‘capacity’.

The most serious limits to achievement are social barriers such as poverty and racism. As Stephen Gould put it:

“I am, somehow, less interested in the weight and convolutions of Einstein’s brain than in the near certainty that people of equal talent have lived and died in cotton fields and sweatshops.”


Part 2, about the “predictive validity” of the new Baseline Tests, will appear soon.

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