Any parent of a teenager knows the brain of a 13-year-old is different than that of a 9-year-old. Pinning down those differences in a scientific way has been elusive—until now. Dr. Jay Giedd, of the National Institute of Mental Health, examines recent findings from magnetic resonance imaging of the teen brain and explores the implications these findings have for parents, teachers, society and the teens themselves. From the Series:2002 Medicine for the Public Lecture Series