IQ is generally expected to remain stable over time, but new research suggests that the measure increases significantly for those with autism during adolescence and early adulthood.

In a long-term study of 126 people on the spectrum, IQ scores increased by an average of 7.48 points between the ages of 12 and 23. During the same period, autism symptoms in those studied remained unchanged.

The findings published Friday in the Journal of the American Academy of Child and Adolescent Psychiatry looked at children who were part of the UK Special Needs and Autism Project, which periodically followed up with a group of kids on the spectrum in England to assess how they changed.

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The study included children with severe intellectual disability all the way up to individuals with IQs in the superior range. They were evaluated at ages 12, 16 and 23.

IQ tests are standardized for each age, so scores are not expected to change as kids get older. The increases seen in the children with autism studied were substantial, the researchers said, enough to be noticed by parents and teachers.

The IQ gains were greatest among those who had a history of early regression in language, the study found. In that group, the increase was 15.4 points compared to just 6.6 points in individuals without regression.

“While we can’t exclude the improvement is partly due to increased motivation or ability to access IQ tests, rather than an intrinsic improvement in learning ability, these alternatives are also important aspects of real-life functioning that may open new educational and employment opportunities for autistic people,” said Emily Simonoff, a professor of child and adolescent psychiatry at King’s College London who led the study.