From How to Lose Your Job on Your Own Time:
Personal disclosure is the norm on social networking sites. But the Pew study included an unexpected finding: Teenagers have the most sophisticated understanding of privacy controls on these sites, and they are far less likely than adults to permit their profiles to be visible to anyone and everyone.
If you are a teenager, restricting public access to your profile has the nice effect of restricting your parents access to your social network data. I suspect lots of teenagers have pictures from parties and other activities that they don’t want their parents to see. This makes me wonder how much the use of privacy controls by teenagers has to do with a desire for more privacy in a general sense versus hiding from mom and dad.
Teenagers are also much more under the control of other authority figures than most adults are. Teachers are a good example of this situation. It is dangerous to speak negatively about your teacher when there is no way to know that they are not following your online activities.
Monitoring how these same teenagers change their privacy settings as they mature and become more independent would be a very interesting study.