'Nearly 1 million children in the United States are potentially misdiagnosed with attention deficit hyperactivity disorder simply because they are the youngest -- and most immature -- in their kindergarten class, according to new research by a Michigan State University economist.

These children are significantly more likely than their older classmates to be prescribed behavior-modifying stimulants such as Ritalin, said Todd Elder, whose study will appear in a forthcoming issue of the Journal of Health Economics.

Such inappropriate treatment is particularly worrisome because of the unknown impacts of long-term stimulant use on children's health, Elder said. It also wastes an estimated $320 million-$500 million a year on unnecessary medication -- some $80 million-$90 million of it paid by Medicaid, he said.'

Read more: Nearly One Million Children in U.S. Potentially Misdiagnosed With ADHD, Study Finds