I'm taking myself out of the expert category of adolescent identity formation. I'm still having a hard time pulling all my research together. Here's what I know so far:
Most identity formation theories are based on Erikson's model of human development. According to him, we go through eight stages, each of which roughly corresponds to a certain age range. The primary task of adolescents, age 12-18, is to determine who they are and who they will be. In pursuing this self-concept, kids have three things to contend with: sexual maturity, occupational skills and talents, and their social context.
James Marcia further refined the model by identifying two key processes that adolescents use in forming their personalities: actively exploring their options and making deliberate choices about those options. The use of these two tools, either separately, in combination, or not at all, describes four phases of identity development. The adolescent who has adopted his or her opinions on sex, a career, and society from a parent or institution without conscious exploration or choice is foreclosed. The teen who is neither exploring nor choosing, but rather living day to day without consideration of the future is diffused. A kid who is actively struggling with these issues is in moratorium, and one who has resolved them has achieved identity. The process is recursive: people can cycle through all the phases several times. A stable identity is not necessarily unchanging; it is however continuous over time.
What does all of this mean to the classroom teacher? Good question.