As a middle school teacher, I heard many times that the frontal lobes reorganize themselves during adolescence. This is used to explain why teenagers make bone-headed decisions, and as a caution to kids not to mess with drugs or injuries during this period. Your question set me to looking for some quick concrete information. There are many books on the subject, but I found an interesting page on the National Institute of Mental Health website.
http://www.nimh.nih.gov/health/publications/teenage-brain-a-work-in-progress-fact-sheet/index.shtml
The NIMH paper reports research saying that there appear to be two major growth spurts of the human brain, one around the time of birth and another shortly prior to puberty. It further suggests that each of these growing periods are followed by a pruning process, while the brain decides which of the new connections are important and which are not. These processes are highly individual from person to person, and they say that it is difficult to make generalizations. Research suggests that the growth of white matter in the brain proceeds typically from the front to the back, at the time of puberty. ". . .studies have suggested that gray matter maturation flows in the opposite direction, with the frontal lobes not fully maturing until young adulthood." That it is followed, over a course of years, by a growth or development of myelin sheathing from the back toward the front. Myelin forms on the outside of neurons and enhances their performance.
Neurologists use functional magnetic resonance imaging (fMRI) to watch the brain non-invasively as it performs tasks. It is truly an amazing and exciting technology. Meanwhile I still advise teens to be careful with their brains.
