What if?: Writing a Short Story

The other day in English class Mr. Allen was talking to me about my short story. In the course of the discussion, the nature and likely responses of teenage boys came up. This was contextual to the likelihood that a teenager would stay and help an older stranger who needed help around the house or yard. Mr. Allen concluded that a kid would mostly like try and succeed in getting out of it, while I tried to defend myself and peers. That got me thinking. What if teenagers were selfless?
The most intriguing change would be in adults' perceptions. If teenagers were selfless, most likely brought on by better communal and self awareness, people like Mr. Allen wouldn't be so sure either of how my character or his students would respond to certain situations. We'd have a better reputation, and be able to take on much greater responsibility at home and in the community. That's not to say there aren't teenagers who don't do such things, this is just a question of perception. It seems like problems with substance abuse and accompanying illicit activities either wouldn't exist, or wouldn't be of concern to parents, authorities, or media, since they'd be assured of our appropriate, adult-like disposition to such activities. Isn't that why "responsible" adults drink?
Then again, there's a reason most teenagers are selfish; they're in the process of becoming selfless. Isn't that what growing up is all about?