IQ levels, long thought to remain relatively stable throughout a person's lifetime, can actually change dramatically—up or down—during the teenage years, according to a new study. Researchers tested teens at 14 and again just before they turned 18, and found that close to a third of them had significantly different scores, the BBC reports. The highest gain was 21 points—enough to raise a person from below average to above average—and the biggest plunge was 18 points.
The researchers also found changes in the teens' brains, making it less likely that the swings in IQ were the result of somebody having a good or bad testing day. The results show that it's a mistake to pigeonhole young students on the basis of IQ tests, say researchers. "We have a tendency to assess children and determine the course of their education relatively early in life," explains the lead researcher. "But here we have shown that their intelligence is likely to be still developing." (Read more high school stories.)