By age five or six, a child's brain is 90 percent the size of an adult's, and for a long time scientists thought that the organ's significant structural growth ended by around 12 years old. Recent research, however, shows that an adolescent's brain makes dynamic changes around that age as well as during all of the teen years. As Leslie Sabbagh explains in our cover story, “The Teen Brain, Hard at Work,” beginning on page 20, areas involved in planning and decision making experience a spurt of growth at 11 or 12 years and then undergo pruning and reorganization through the early 20s.
That is why, when faced with complex choices under time pressure, the immature cognitive systems can overload, sometimes with catastrophic results. “It's not just that one thing goes wrong,” a frustrated parent of two teenagers recently groused to me. “It's that an astonishing chain of bad decisions can occur at the same time.” While parents wait for nature to take its corrective course, at least they can take comfort in knowing that sheer rebelliousness is not solely to blame.