Approximately 6.4 million children ages 4 through 17 have received a diagnosis of A.D.H.D at some point in their lives. According to this New York Times article, that's a 53 percent rise in the past decade. And which group tends to get diagnosed the most? Poor kids. Children covered by Medicaid "have among the highest rates of A.D.H.D. diagnoses: 14 percent for school-age children, about one-third higher than the rest of the population."