IQ Scores of Teens May Change Over Time

Oct. 19, 2011 -- A teen's IQ is not set in stone, according to a study published today in Nature. Instead, the standard measure of intelligence -- often used to predict future success -- can fluctuate dramatically.

"The results indicate that an early developer doesn't necessarily continue to excel; and a late developer can catch up. Educators already know this," study researcher Cathy Price, PhD, tells WebMD in an email. "The more relevant point is that, if IQ changes are real (as we claim), they are not measuring a capacity to do well. They are measuring how well the individual is doing at a fixed time."

Price, a professor at the Wellcome Trust Centre for Neuroimaging at University College London, and colleagues, tested 33 "healthy and neurologically normal" adolescents aged 12 to 16. Their IQ scores ranged from 77 to 135, with an average score of 112.

Four years later, the same group took another IQ test. While the average score of 113 was only one point greater than the previous test, the range of scores was quite different: 87 to 143. Individually, the results were quite striking, as participants showed as much as an 18-point drop in IQ, while others shot up as high as 21 points.

The researchers also broke down the scores by verbal IQ, a measure of language, arithmetic, general knowledge and memory, and performance IQ, which focuses on visual problem solving. Scores fluctuated by as much as 23 points in verbal IQ and 18 in performance IQ.

"A change in 20 points is a huge difference," Price says. "If an individual moved from an IQ of 110 to an IQ of 130, they move from being 'average' to 'gifted.' And if they moved from 104 to 84, they move from being high average to below average."

Overall, the researchers report, one-fifth of the kids tested moved from one IQ category to another, from average to below average, for example.

Brain Changes

Each of the participants also underwent brain scans -- a combination of functional and structural imaging -- at the time that they were given the IQ tests.

Decreases or increases in the density of gray matter in a region associated with speech corresponded with better or worse verbal test scores. Similar changes were noted in the area of the brain tied to hand movement among students whose performance IQ scores had shifted.

Those scans, Price says, confirm the researchers' findings that the changes in test scores are likely real.

"When we saw the fluctuations in [IQ test] performance, we were concerned that this was measurement error (e.g. differences in concentration on the different testing times)," Price says. "However, then we found that the degree to which verbal or nonverbal IQ changed was mirrored by changes in brain structure."