IQ, originally thought to be static, has long been proven changeable. And while education has similarly long been known to correlate with higher IQ, the relationship wasn’t clear — did more schooling lead to increased IQ? Or were people with higher IQs just more likely to stay in school?

Each year of schooling equals a “small but noticeable” boost in IQ, a new meta-analysis of 42 existing studies.

“Our analyses provide the strongest evidence yet that education raises intelligence test scores,” says study author and psychological scientist Stuart J. Ritchie, of the University of Edinburgh. “We looked at 42 datasets using several different research designs and found that, overall, adding an extra year of schooling in this way improved people’s IQ scores by between 1 and 5 points.”

He added that the positive effects of education on IQ endured far beyond the school years; studies of people who took intelligence tests in their 70s and 80s maintained IQ gains made during their school years. This is supported by research that has found childhood and adolescence to be the time in life during which IQ is most elastic, whereas repeat tests in adulthood tend to give the same IQ result.

But these findings beg the question — do they matter? IQ test scores are certainly one measure of increased intelligence, but only one — and a problematic one at that. First, IQ tests might yield steady results for adults, and thereby provide a more complete understanding of an individual’s intelligence. But in childhood and adolescence, the results of repeated tests are can vary widely — by “20-plus IQ points, one way or another,” says Stephen Ceci, a professor of developmental psychology at Cornell University. Using such an unpredictable evaluation of children’s intelligence — and by extension, the success of schooling — to “inform educational policy and practice,” as the authors seem to hope, is risky and undependable.

Also risky is the use of IQ to measure intelligence at all. Many IQ tests reward the ability to taxonimize, that is, to group things by likeness rather than by association. (For instance, taxonomic reasoning would group a chair and sofa together, because both are pieces of furniture, whereas thematic reasoning groups a sofa and a house, because a sofa would be found inside a house.) This type of reasoning is more common in the West, and traditional educational models there explicitly teach the skill, which could be behind the link between education and increased IQ; it is likely that most of the research Ritchie and coauthor Elliot Tucker-Drob, of the University of Texas at Austin, drew from research focused on Western populations. (Other explorations of intelligence question whether taxonomic reasoning is so integral, or rather a culturally ascribed quality of ‘smarts.’)

While it’s great that there is evidence that definitively proves schooling improves intelligence, given the problems around the concept and measurement of IQ, perhaps a better informer of policy and practice is simply the fact that intelligence can change — given the right mindset.