There's no blood test or brain scan for attention deficit hyperactivity disorder, so doctors rely on checklists. ABC News chief health and medical editor, Dr Richard Besser, says these are some signs that your child may have ADHD -- inattention, inability to concentrate, hyperactivity, and impulsivity.
"You look for problems not just in school but problems at home, problems with peers," he said. "So if you're only seeing it in school it may be a school readiness issue."
That school readiness issue may lead to an increase in ADHD diagnoses. A new study out of Taiwan showed that younger children in class are more likely to be diagnosed than their older peers.
When you go from oldest to youngest, the rate of diagnosis goes from 1.8-percent to 2.9 percent.
Besser says maturity issues and ADHD may show up in similar ways, especially in the earlier grades.
So how do you know if your child is ready for school?
"I'll look to see can they sit still," said Besser. "Can they follow directions? Can they pay attention? And it may be for some of those children that may be on the cusp starting so early isn't a good way. It's better for them to wait another year."
The study also found the results were the same for both boys and girls. And the youngest children were more likely to be diagnosed and given medication than the oldest children.
Click here to read more about the study published in the Journal of Pediatrics.