The grammar school fallacy

No fallacy dominates popular attitudes to education like post hoc ergo propter hoc ("after this, therefore because of this"). Y follows X, so X must have caused Y.

Consider three common lines of reasoning. Much of the British elite went to Oxford and Cambridge, therefore Oxford and Cambridge must be the best universities and ambitious youngsters should therefore strive to get into those institutions. University leavers tend to get higher paying jobs, therefore a university education must give young people the skills necessary to secure such employment, and therefore almost all young people should go to university.

And because grammar schools produce children with excellent exam results, that must be because grammar schools are excellent schools, and we should wish to see more of them. Post hoc ergo propter hoc.

But it ain't necessarily so. What if the 18-year-olds who go to Oxford and Cambridge and other Russell Group universities are already bright? Perhaps those particular institutions aren't really adding very much in academic terms at all.

What if university leavers already had many of the skills required to thrive in the modern workplace before they arrived? Perhaps a university education doesn't actually confer those abilities after all, and that from an economic perspective, it's a waste of resources to cram ever more young people through this particular form of higher education.

To identify whether a particular factor causes an outcome, we need to consider the counterfactual. In other words, to ask what would have happened in the absence of that factor? Establishing counterfactuals is tough but, to be credible, an analysis has to at least attempt it.

Now let's consider the case of the 164 grammar schools in England, which select girls and boys at age 11 on the basis of their academic ability. There's no question that the 167,000 students who attend them get better GCSE and A level results on average, relative to the roughly three million pupils who attend nonselective state schools. But is that because of the quality of the teaching at the schools themselves and their selective mechanisms? Or is it because of the pre-existing abilities of the children who attend them, perhaps because they come disproportionately from well-off families? What's the counterfactual? Might those children perhaps have gone on to do well anyway in another school environment, such as a comprehensive? Research from Durham University suggests a definitive answer to that.

When the academics make statistical adjustments for the prior abilities of students and the wealth of their family background (grammar schools do tend to be dominated by the middle classes), they find little evidence that these schools add much.

However, there is some pretty compelling statistical evidence that poorer children in regions such as Kent, where grammar schools are still relatively common, have worse academic results than one would otherwise expect. This suggests brighter children with wealthier parents tend to drive up overall standards in comprehensive schools. But the corollary of this is that the presence of grammar schools is indirectly harmful to the wider local schools system. "Grammar schools in England endanger social cohesion for no clear improvement in overall results," concludes Durham's Professor Stephen Gorard.

When she became Prime Minister in 2016, Theresa May promised she would allow the establishment of new grammar schools. For the first time since the mass comprehensive conversions of the 1960s, the government planned to encourage them. The evaporation of her authority after last year's election fiasco has forced May to retreat from that. Yet it remains Government policy to allow existing grammar schools to expand, in itself a significant departure from the cross-party policy consensus of the past 40 years.

Many of those who want to expand academic selection at age 11 (though not all) are inspired by decent motives. They not only look upon the good academic results produced by grammar schools and wish to proliferate that success, but also observe that the post-war era of expanding grammar schools was also an era of rising social mobility, when it felt like talented young people from modest backgrounds could "get on".

Yet they may have been tripped up by another statistical fallacy: confusing correlation with causation. Was the acceleration of social mobility of this era due to the introduction of grammar schools in the 1944 Education Act? Or more "room at the top" in British economic life, as white-collar work and the professions expanded rapidly thanks to rapid technological change? The evidence leans to the latter.

The question of how to resurrect the social mobility of the post-war era is a complex one. But when it comes to education, the most statistically rigorous research we have (drawing on the research of economists, psychologists, neuroscientists and statisticians) strongly suggests the key to boosting lifetime attainment lies in improving (very) early years care and in targeting resources on the least advantaged.  If ministers really care about the life chances of the poorest, they should invest heavily here, reverse the post-2010 cuts to Sure Start funding, and, finally, shed those beguiling grammar school fallacies.