After more than 50 years leading the fight to legitimize attention deficit hyperactivity disorder, Keith Conners could be celebrating. Severely hyperactive and impulsive children, once shunned as bad seeds, are now recognized as having a real neurological problem. Doctors and parents have largely accepted drugs like Adderall and Concerta to temper the traits of classic A.D.H.D., helping youngsters succeed in school and beyond. But Dr. Conners did not feel triumphant this fall as he addressed a group of fellow A.D.H.D. specialists in Washington. He noted that recent data from the Centers for Disease Control and Prevention show that the diagnosis...