This post summarises the arguments in the fifth chapter of my new book, Making Kids Cleverer. The rest of the chapter summaries can be found here.

If intelligence is casually connected with heath, happiness and safety, if the environment matters in determining how intelligent we end up, how can we go about making ourselves cleverer?

One thing we can be fairly sure will raise children’s intelligence is sending them to school. Education and intelligence have a two-way interaction: the more intelligent you are, the longer you stay in school and the longer you stay in school, the more intelligent you become. The evidence supporting these claims is reviewed as well as the two main objections. The first objection is that gains to intelligence are temporary and tend to disappear over time. Although attempts to raise IQ through preschool interventions seem to quickly fade, a recent meta-analysis has shown that increases in IQ brought about by changes to educational policy are very durable, lasting at least until people reach their 70s.

The second objection is that gains to intelligence are hollow. It’s well known that anyone can improve at anything through practice; this applies to taking IQ tests as much as anything else. If you practise taking IQ tests, your score will go up, but will you be any more intelligent? Measured intelligence may not be the same as genuine intelligence. Maybe the effects of education on IQ are due to the kinds of knowledge schools teach. If a test asks what an apple and an orange have in common, full marks are awarded for classifying them both as fruit, but only half marks for pointing out their shape, taste or that they contain seeds. But, although knowing how to think abstractly is rewarded by IQ tests, it also has real-world advantages. 

The effect that school has to increase children’s crystallised intelligence. What we think of as intelligence can be broken down into two major components: fluid and crystallised. Fluid intelligence is our raw reasoning power. It’s usually defined as the ability to handle data and use logic to solve novel problems without relying on prior knowledge. It includes the capacity to store new information in long-term memory and is correlated with working memory capacity as well as our ability to focus our attention and impulse control. Crystallised intelligence is the ability to access and utilise information stored in long-term memory. This includes our vocabulary, knowledge of arithmetic and understanding of how the world works, as measured by questions like, ‘Why do streets have consecutively numbered houses?’

While both these aspects of intelligence are correlated with each other, their separate existence has important implications for making kids cleverer. No matter how poor you are at reasoning or solving abstract problems, you can still commit facts to long-term memory. Fluid intelligence governs how much information we can process at a given time, and because we can only remember what we think about, it stands to reason that those who think more quickly will end up remembering more. This does not imply that children with lower fluid intelligence cannot remember, just that they may need more repetition and patience. Happily, knowledge is cumulative: the more you learn about a subject, the easier it becomes to remember additional related items of knowledge.

From here, I go on to examine the fact that IQ scores rose steadily and dramatically throughout the 20th century. Clearly, evolution cannot have an effect in such a short span of time so our biology has remained more or less unchanged; perhaps then the changes have been cultural? This is the thesis of James Flynn who first studied the rise in IQ scores and gave his name to what has become known as the Flynn effect. And the most surprising thing about these gains is that it seemed as if it was fluid intelligence not crystallised intelligence that was increasing most. Flynn’s hypothesis is that social pressures reward acquiring skill in certain areas disproportionately more than in others, and that the biggest social change over the period of these IQ increases has been the increasing tendency to view the world through ‘scientific spectacles’ and think in more abstract terms.

It should be obvious that any rise in IQ scores does not mean that people living today are cleverer in any functional sense than our ancestors. People in the past thought in ways that were suited to the world in which they lived, and so do we. You might think this is a bit of a trick and evidence that IQ tests don’t actually measure anything important, but it turns out that the kind of thinking that allows us to do better in IQ tests has important real-world applications. The ability to divide the world into scientifically useful classifications, think hypothetically and frame our thoughts in abstract, universal terms seems to lead to us making better moral decisions. 

There is, however, a potential downside to all this. Even if the ability to think hypothetically generally allows us to be more empathetic, the fact that children are often ignorant about basic facts about the world in which they live severely curtails their ability to think rationally.

The rest of the chapter is spent addressing various approaches that some people believe might raise children’s intelligence including growth mindset interventions, brain training, thinking skills programmes and ability grouping in schools. The evidence for each is reviewed and all are found wanting.