They only have as much sense as they experience/as their parents have. You have someone cheering you on, giving you support or attention for fighting, guess what you're going to want to do more of?

Think about a mid-teen's life nowadays. They have home and school. That's it. They can't drive/get away and school gets more and more regimented and restrictive and if they have problems at home too (what do you do, for example, if you are getting bad grades and have teachers/school on top of you and parents? You only have access to your friends/peers when they say or when you "break out" and get together anyway) then you're in a pickle.