In "A Separate Peace" why is Finny's nonconformity accepted by the other boys, while Leper's is not?
To sum it up in a very simplistic way, Finny is cool and Leper is not. Leper doesn't quite fit in socially; he is awkward, laughs at nerdy things, likes nerdy things, and is never quite at ease with other people. He is strained and stiff and doesn't like doing sportsy, fun things that the other boys do. His interests, appearance, and social demeanor make him an uncomfortable social contact, one who doesn't add fun, spontaneous adventure to a situation. He's kind of a fuddy-duddy that rains on people's parades.
Finny on the other hand is very comfortable around other people; he has a talent for making each person in a group feel welcome and cool. He does things that are outrageous in a super cool, going-against-authority type of way that boys of that age strive for themselves but often don't have the courage to do (the pink shirt, the tie for a belt, etc.). He also invents really fun sportsy games for everyone and has an infectious personality that draws everyone in to the adventure. He's a people-person. He likes things that are fun. His appearance, personality and demeanor are all inviting and interesting.
So, even though both boys do things that are a bit different, Finny's is done with his engaging personality and spunky fun, whereas Leper's is done in a weird, awkward sort of way that no one is really interested in. They are two completely different personalities, and that contributes to the differences. I hope that helps; good luck!