Our brain's maturation follows an intriguing 20-year rhythmic trajectory that helps to explain child and adolescent behavior. To simplify a complex process, this development encompasses two distinct 10-year periods—a childhood acceptance of dependence, and an adolescent reach for independence.

Each 10-year developmental period begins slowly and awkwardly with a four-year initial activation of the brain systems that process the focus of that period, followed by a six-year developmental drive towards confident competence. Think of the four preschool years followed by the six K-5 years, followed by the four middle school years followed by the six high school and early college years.

Our brain is basically a social system. Even a simple task involves the collaboration of many of our brain's hundreds of systems and subsystems. For example, separate subsystems within our visual system process quantity, color, shape, location, and movement. Their collaborative activity can lead to the perception of a red ball rolling across a table—which may spark our brain's decision-making systems to grasp the ball, and our motor system to carry out the action.

These hundreds of cognitive systems don't mature simultaneously. Children can grasp before they can walk, and talk before they can read. Similarly, the early adolescent brain can successfully carry out many but not all the functions of a mature brain.