National Geographic has an interesting article up about Teenage Brains.

The first full series of scans of the developing adolescent brain—a National Institutes of Health (NIH) project that studied over a hundred young people as they grew up during the 1990s—showed that our brains undergo a massive reorganization between our 12th and 25th years.

The article details some of those changes that come with maturation, including the development of the frontal areas associated with goal setting and the linkage between the hemispheres strengthening. The effect of these changes is to allow the consideration of a broader array of "variables" in decision making.

The author states,

When this development proceeds normally, we get better at balancing impulse, desire, goals, self-interest, rules, ethics, and even altruism, generating behavior that is more complex and, sometimes at least, more sensible. But at times, and especially at first, the brain does this work clumsily. It's hard to get all those new cogs to mesh.

Teens are just beginning to be able to use these new neural networks, which can help to explain the inconsistency of behaviors and moods in adolescence.

Abigail Baird, a Vassar psychologist who studies teens, calls this neural gawkiness—an equivalent to the physical awkwardness teens sometimes display while mastering their growing bodies.

Sensation seeking and interest in novelty peaks around age 15. Neuroscientists see this as an important adaptive component of brain development; it provides useful experience for adulthood. The risk taking that often accompanies this desire results from a difference in valuation of risks and rewards; adolescents value the reward greater than do adults.