As the mother of two sons who went through adolescence and a practicing neurologist, Frances E. Jensen offers a valuable perspective on teenage behavior. Dr. Jensen explored the neurological research--including insights gained from recent advances in functional magnetic resonance imaging--and found that the adolescent brain is both more powerful and more vulnerable than at any other time of life. Because they have many more synapses than adults, teenagers are able to learn more efficiently. At the same time, teenagers have not yet built strong connections between the frontal lobes--the seat of executive function, judgment, empathy, and impulse control--and the rest of the brain, where emotions dominate. Teenagers cannot yet access their frontal lobes for instant decision making--leading to actions that so often leave parents and teachers wondering, "What was he thinking?" In this interview with Educational Leadership, Dr. Jensen describes some differences between typical teen behavior and more serious mental illness, outlines factors causing high anxiety among teens these days, and advocates empowering young people by giving them the facts about brain development and the biological reasons behind how they feel and what they do.