(WHTM) — When you hear about ADHD — attention-deficit/hyperactivity disorder — you may think of a child struggling to sit still in class or drifting off in the middle of a lecture. But a new study shows ADHD symptoms often come in waves, even when kids become adults.

Researchers at the University of Washington followed 558 people with ADHD for 16 years and found about 90% of them had some symptoms of the disorder, usually off and on, up until age 25. By the end of the study, only about 9% were steadily symptom-free.

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ADHD may look different depending on what stage of life one is in. Younger children may show more signs of hyperactivity, like trouble sitting still and interrupting others. Older kids and young adults may have trouble paying attention or completing tasks they find boring.

This is the first study that measures ADHD symptoms at multiple points throughout childhood and into young adulthood. Since ADHD signs may come and go, it’s important that people with ADHD and their loved ones are aware of times when they might need more support, especially when stressful situations arise.

If symptoms return and make life more difficult, talk to your doctor.