Let me preface this whole blog by saying that stereotyping is wrong. Not everyone in a particular group is the exact same, nor should we treat them that way.
That said, I have have a theory as to why teenagers seem to think they know everything. In reality, we see the same thing in a lot of adults, but I'll get into that later.
In my Adolescence Class, we learned that before children become adolescents they generally only thought concretely, meaning that they had a hard time with symbols and "what if" questions. They could imagine fairies and dragons, but had a harder time with, "what would my life look like if I...?" Between the ages of ten and thirteen, and really on until they get to be twenty five for boys, and I think twenty one for girls, adolescents' brains grow at significant rates. One of the first abilities they gain is the ability to imagine their life 'if' they did whatever.
Now, let's leave adolescents for a moment and think about some adults. Let's use me, I'm a pretty good test subject for this. I'm in college, and am learning like crazy all the time. I know, that in the grand scheme of things I know nothing, but I sure do like to sound like I know stuff when I think I am starting to understand a theory (see above paragraph if you don't believe this statement). Now, I'd like to say that I think I'm a fairly intelligent person, and that I probably do know a little. I do think through things, and I usually have a pretty good handle on them, but I have to be honest in saying that occasionally, my dad or whoever I'm talking to, will ask a question that will stump me, and then I have to go back to the research table. But for a while, I honestly believe anyone I'm arguing with is wrong because I go to college, and I've really learned something...
Back to adolescents! Their brains just grew like crazy. Only a few years ago they couldn't imagine what their own lives would be like, now they can think about all of that stuff and experiment with it, and can think abstractly about world issues, and global warming, and war, and friendships, and that their parents might be wrong. And the more they think abstractly about something, the more they understand it, and if their parents disagree, the more the adolescent think his/her parents must be wrong. Why? Because teenagers are frickin' brilliant. Look at how much they've learned in such a short amount of time. Have their parents made a similar jump in the past few years? They have not. So, the teenager must have really learned something and must pass it on to the world. Especially their illiterate parents.
I don't think teenagers are much different than us. When they learn a little something, they think they've really got something, just like we do. Now, they lack the life experience that allows them to look at what little they learn and say, "Compared to EVERYTHING I don't know, this really isn't much, is it?" But I argue that if we didnt' have that life experience we would act in much the same way as they do.
Now if I can just remember that when I'm a parent of a teenager...