Intelligence is often thought to be fixed across the lifespan, and IQ scores are used to sort children and adolescents for educational purposes. But in fact, IQ fluctuates, and individuals can be trained to perform better on IQ tests, indicating that sorting on this basis may not serve any useful purpose.

Is IQ stable across the lifespan?

Intelligence is typically measured with standardised verbal and non-verbal reasoning tasks, providing an intelligence quotient (IQ) score that takes account of age. This score is thought to reflect a range of cognitive skills that indicate an individual’s learning aptitude. It is often assumed that IQ is stable across life, with some individuals having higher intelligence than others. These scores are sometimes used to determine a child’s entry to school or a teenager’s place at university, seemingly demonstrating the individual’s ability to achieve.

However, individual IQ scores actually fluctuate, with changes in the brain’s structure and function mirroring changes in IQ. This means that if a child is top of their class on an IQ test at age 11, by the time they are 16, this may no longer be the case. And yet 164 UK grammar schools and many private schools select children on the basis of reasoning (and sometimes maths and English) tests for entry at age 11.

“Individual IQ scores actually fluctuate, with changes in the brain’s structure and function mirroring changes in IQ.”

Studies with childrenadolescents, and adults, have shown that performance on IQ tests can improve with training, further demonstrating that these tests do not measure an underlying fixed ability. Generally the participants in these studies have got better at the task they were trained on, with some transfer to similar tasks, but no transfer to dissimilar tasks (a pattern like the one typically observed following executive function training).

More on transfer
Working memory training in school

Should school entry be determined by tests?

This further calls into question the decisions of schools and universities to determine entry based on performance on these tests. Those who have practiced and received tuition are likely to perform better. Concerningly, it is likely that those who can afford it will pay for tuition in order to get their child into their school of choice. Those families who cannot afford the extra lessons may miss out on the opportunity to send their child to their desired school.

This is all the more disheartening when it is possible that, given the lack of transfer, the training may not even have an impact on school- or university-related abilities or final grades. Further research is needed to investigate the extent to which performance on entrance tests relates to later exam performance, and whether or not those who received initial training do indeed perform better later on.

“The sorting of children according to test performance, regardless of the utility of this approach for determining their learning capacity, may have negative consequences.”

The sorting of children according to test performance, regardless of the utility of this approach for determining their learning capacity, may have negative consequences. Those children who do undergo additional tuition are spending time away from other activities which may be more fulfilling. Children who take the test may feel anxious about their performance, and may then be sorted into a different school from their friends or siblings, potentially leading to loneliness. Those who are not selected for the school they want may also lose confidence in their ability to perform well.

Given these possible outcomes, and considering the need for more research, conversations about why this testing exists and what it seeks to achieve must continue.


  1. With respect, Annie, those who hold on to the idea that IQ is ‘fixed across the lifespan’ should be regarded in the same league as ‘flat-earthers’. Intelligence is not fixed and as recent research has shown, it is not only subject to variation through the natural processes your piece identifies, but also highly susceptible to development/improvement by the systematic application of certain teaching strategies.

    It is well known by teachers working in areas where selection for grammar schools remains that, just as you write, “IQ fluctuates, and individuals can be trained to perform better on IQ Tests.“ This is the precise reason why parents pay for private tutors to prepare their child for taking the test and why schools are restricted in the extent to which they can prepare children in school time. The grammar school system is predicated on the idea that it is possible to give a numerical value to intelligence and that intelligence is fixed, thus justifying selection at 11+. That said, I still disagree with your view that “sorting on this basis may not serve any useful purpose.” It is at least offers an objective view about mental performance, even if it fails in regard to its robustness over time and it serves the precise purpose of differentiating, at a given point, those students who seem to have capabilities that grammar schools recognise are required for their more intensive academic delivery system.

    The assumption that some individuals have higher intelligence than others in fact describes a truth that has been evident throughout human history. It may be an idea that is uncomfortable to entertain, but it is nonetheless true. We are no more equally intelligent than we are equally tall, sporty, artistic, etc. If we accept the premise that both nature and nurture contribute to our makeup in different ways, to a different extent and at different times in our development then plastic intelligence accounts for the different outcomes.

    1. Good to hear from you again John, thanks for your comments. I think the main problem is that we don’t know if IQ tests do indeed offer “an objective view about mental performance” because the research linking entrance test performance and ability to perform at school has not been done. Those who have been trained to perform better on the entrance test do not necessarily then perform better in school – they have likely been trained to do a very specific type of problem that may have little relevance to school studies. The other problem for me is the stress and anxiety that these tests can cause, particularly for those who do not get in.

      I’m interested in your comment about grammar schools having a more intensive academic delivery system. As someone who went to a grammar school, I didn’t feel that it was particularly intensive. We had sets with students separated according to their ability; not all students were given the same level of delivery. I can only compare this with the non-selective secondary schools that I’ve spent time in as a researcher, but overall I haven’t noticed any differences in delivery. It would be interesting to find out more about what actually differs in teaching practices between grammar and non-selective schools.

      I agree that we need to accept the importance of both nature and nurture, and ideally use what we know about the impacts of nature and nurture to guide practice in the classroom (for example, through precision education in the future).

  2. We need more research on the effects of high stakes school entrance tests on mental health.

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