Outside with his friends, Myles Dumas has energy to spare, but at school it was a different story.

"He wasn't focusing. He was always sleeping in school, so that kind of made me concerned in the beginning," said mom, Therese.

Myles' mom and his teachers thought he had ADHD.  He tried three different medications, but nothing helped.

"I was falling asleep in class," he said.

"As a parent, it was frustrating wanting to help him, needing to help him, but not knowing how to help him," said Therese.

It wasn't until doctors performed a sleep study that the problem became clear: Myles had a sleep disorder.

"Many of the kids with a sleep disorder will present with inattention. They'll have fatigue. They may even look like a child who has attention deficit hyperactivity disorder, but in fact, it's related to their sleep," said Thomas Burns, a neuropsychologist.

A sleep study can identify sleep apnea or other problems that may look like ADHD.

If your child snores, has restless sleep, difficulty falling asleep or daytime fatigue, don't assume it's ADHD, talk to your pediatrician.

"The really important message for parents is if there's any problems during the day that might sound like attention deficit, then think about their child's sleep," said Dr. Gary Montgomery, a pediatric sleep medicine specialist.

Myles was diagnosed with narcolepsy. Now, medication is helping him stay awake and stay focused on his schoolwork.

For children who really do have ADHD, the American Heart Association is  now recommending those patients be screened for heart conditions before going on some ADHD drugs.