During teenage years, IQ - the standard measure of intelligence can increase or fall significantly and these changes are associated with changes to the structure of the brains, finds study.
The findings may have implications for testing and streaming of children during their school years.
The researchers at the Wellcome Trust Centre for Neuroimaging at UCL (University College London) and the Centre for Educational Neuroscience, led by Professor Cathy Price, tested thirty-three healthy adolescents in 2004 when they were between the ages of 12 and 16 years.
They then repeated the tests four years later when the same subjects were between 15 and 20 years old. On both occasions, the researchers took structural brains scans of the subjects using magnetic resonance imaging (MRI).
Professor Price and colleagues found significant changes in the IQ scores measured in 2008 compared to the 2004 scores.
Some subjects had improved their performance relative to people of a similar age by as much as 20 points on the standardised IQ scale; in other cases, however, performance had fallen by a similar amount.
According to Professor Price, a Wellcome Trust Senior Research Fellow, it is not clear why IQ should have changed so much and why some people's performance improved whilst others' decline.
It is possible that the differences are due to some of the subjects being early or late developers, but it is equally possible that education played a role in changing IQ, and this has implications for how schoolchildren are assessed.
"We have a tendency to assess children and determine their course of education relatively early in life, but here we have shown that their intelligence is likely to be still developing," says Professor Price.
"We have to be careful not to write off poorer performers at an early stage when in fact their IQ may improve significantly given a few more years," he added.
The study was recently published in the journal Nature.