The National Institutes for Mental Health estimates 3 to 5 percent of children have Attention Deficit Hyperactivity Disorder. That means in a classroom of 25 to 30 children, it's likely at least one has ADHD. It's a behavioral disorder resulting in the inability to pay attention for a period of time.

"They hear the bird. They hear the door closing or someone talking. So it's kind of like having an orchestra around you with music playing all the time, and you're trying to read or concentrate on one thing," says Psychologist Dr. John Braccio.

According to Dr. Braccio, the exact cause of the neurological disorder is unknown. But in a recent study released by the journal, Environmental Health Perspectives, one-third of ADHD cases are linked to either prenatal exposure to cigarette smoke or childhood exposure to lead.

"I don't think there is any doubt though that people who are exposed to smoking or toxic type materials that this can certainly have an impact on the person," says Dr. Braccio.

While ADHD can be difficult to live with, there are treatments that include medications like Ritalin and Adderall.

"In order for them to pay attention they need to be more stimulated,” says Dr. Braccio. “That's why people with ADHD can be very successful on the positive end.”