James Flynn's research on the eponymous Flynn Effect, showing massive gains in IQ in 14 nations in the course of the 20

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Century, was leapt on by hard-working teachers, social policy wonks and dieticians. It rebutted claims that IQ was immutable and implied that ambitious interventions in families and schools could be effective. The gains Flynn discovered were so large, they suggested an average child would be regarded as a ‘genius’ by their great grandparents.

However, Flynn has now changed his mind. In a speech he gave earlier this year at the International Society for Intelligence Research, and now published in Intelligence, a peer-reviewed academic journal, Flynn announced that this forward movement in IQ scores across the West has been slammed into reverse. In some nations (like the USA) the increase has continued. But, starting in the mid-90s, other nations have gone backwards (e.g. Sweden). According to Flynn’s latest findings, the Nordic nations are projected to see national intelligence scores drop by a total of seven points by 2025. Scores in other European nations are mostly flat, with some odd bouncers, like the Netherlands, which shows no change in pre-schoolers, mild losses in high school, and possible gains in adulthood.

In the UK, IQ scores for the very highest-achieving children have started to decline, says Flynn. That is, the best are no longer as exceptional as they were. Huge, if true: IQ scores are linked to a nation's economic power, and reflect (and are reflected in) the effectiveness of society at every level, from family stability to creative achievement.

The obvious question raised when Flynn first disclosed that IQ scores had risen by between 20-30 points over the 20th century was, ‘What's the limit?’ Social scientists were generally optimistic – it looked as though the right sorts of interventions could actually raise IQ. A current example is systematic synthetic phonics, which has apparently boosted reading skills across England. In maths, sharing ideas such as mapping intuitive magnitude (‘that slice of cake is bigger’) on to squiggles like ‘7’ and ‘9’ allows children to compress five thousand years of cultural development and learn mathematics in a few short years. We are learning machines – we can stand on the shoulders of giants.

But hang on a second. What becomes of this optimism if it turns out that IQs are now falling across the developed world? What is going wrong, exactly, for the brightest children in the UK? Sadly, research on cognitive ability in the UK, especially longitudinal studies stretching back several generations, has not been a priority. But the data we have on the Netherlands, where these sorts of studies are more common, indicates that while the Dutch are doing an excellent job of educating average children, the most able are also falling behind. Which suggests that getting our schools to do more for the brightest kids might be part of the solution.

What James Flynn is highlighting in this latest research is that a nation’s IQ doesn’t just go in one direction. Something has happened in the last decade or so that has put progress into reverse in some countries and failed gifted children in others. We need to find out why and what to do to make sure its upward trajectory is restored.

Timothy Bates is a Professor of Differential Psychology at Edinburgh University