A comprehensive study released today by the Mayo Clinic found Attention-Deficit Hyperactivity Disorder, or ADHD, affects 7 and a half percent of school age children. Prior research has found widely varying percentages of students with ADHD, but Mayo researchers are confident they have an accurate number given the scope of the project. The research also found that ritalin and other stimulants used to treat ADHD were rarely prescribed to children without the disorder. Minnesota Public Radio's Laurel Druley has this report.