A 15-year-old girl and her parents recently came in for a chat with Dr. James Perrin, a Boston pediatrician, because they were concerned about the girl's grades. Previously an A student, she was slipping to B's, and the family was convinced attention deficit hyperactivity disorder was at fault — and that a prescription for Ritalin would boost her brainpower. After examining the girl, Perrin determined she didn't have ADHD. The parents, who had come in demanding a prescription, left empty-handed. Perrin, a professor of pediatrics at Harvard Medical School and spokesperson for the American Academy of Pediatrics, and other physicians...