There are several reasons to explain this.
First, teenagers enjoy being in a group of people who agree about things, they don’t want to be discriminated against and be pushed away from the group, therefore they will follow their peers’ behaviour. My personal experience attests to this: Before I met those bad peers, I was a good student who studied very hard and seldom played online games. After I met them, I became a bad student who skipped the classes and always played online games, as I don’t want to be different, I want to be as same as them. Even I wanted to study, I would try to give up my mind.
Second, is about independency. Teenagers are not children anymore, they want to grow up, get rid of their parents’ control, therefore they will prefer to listen their peers’ opinion rather than their parents’ opinion. This time, my personal experience also attests to this: My parents wanted me to have a good academic performance at school, they needed me to study every moment. Meanwhile, those bad peers wanted me to play with them, they didn’t want me to study. They told me that study was a kind of wasting my time and my youthhood. So what next? Of course I chose to listen my peers’ opinion.
Third, is about curiosity. Teenagers are curious about everything, they may follow their peers’ behaviour as they want to satisfy...