The brain of a pre-teen or adolescent is a brain still in the process of maturing. New research has shed some new light on this ongoing maturation. It seems that the young person who is more able to resist peer pressure may have stronger connections between various areas of the brain. This makes them able to make more mature decisions than their counterparts.
"Professor Tomas Paus and colleagues at The University of Nottingham used functional neuroimaging to scan adolescents while they watched video clips of neutral or angry hand and face movements. Previous research has shown that anger is the most easily recognised emotion."
Functional neuroimaging showed that the areas of the brain used to plan and read social cues were stronger in those pre-teens and adolescents who were more able to resist peer pressure. The prefrontal cortex of their brains also showed more activity. The prefrontal cortex handles decision-making and the suppression of inappropriate behavior.
http://www.sciencedaily.com/releases/2007/07/070725093605.htm