The mental ability of teenagers can improve or decline on a far greater scale than previously thought, according to new research. Until now the assumption has been that intellectual capacity, as measured by IQ, stays quite static during life. But tests conducted on teenagers at an average age of 14 and then repeated when their average age was nearly 18 found improvements - and deterioration. The findings are published in the journal Nature. They have implications for how pupils are assessed, and the age at which decisions about their futures are made. This study involved 19 boys and 14 girls, all undergoing a combination of brain scans and verbal and non-verbal IQ tests in 2004 and then in 2008. The results show that a change in verbal IQ was found in 39% of the teenagers, with 21% showing a change in "performance IQ" - a test of spatial reasoning. The findings are seen to have greater validity because for the first time the variations in IQ correlated with changes in two particular areas of the teenagers' brains. An increase in verbal IQ corresponded with a growth in the density of part of the left motor cortex - a region activated during speech. And an increase in non-verbal IQ correlated with a rise in the density of the anterior cerebellum - an area associated with movements of the hand. The work was led by Professor Cathy Price of the Wellcome Trust Centre for Neuroimaging at University College London and is published in the journal Nature. The paper suggests that the results could be "encouraging to those whose intellectual potential may improve and a warning that early achievers may not maintain their potential". Professor Price said: "We have a tendency to assess children and determine the course of their education relatively early in life. BBC