[Sorry, I'm still catching up with my old email.] Seems like the problem is the classroom itself. Or, really, the setting of the classroom. At L-S in the Computer Center, different people were at different "levels" and it was fine. I was still terrible at chess, but I didn't care. But, maybe, people who hung out at the Computer Center were self-selecting and, in a different context, people wouldn't naturally just mix it up. I remember Michael Teixeira not hanging out at the Computer Center after a while because he was afraid of being called a "computer fag". Perhaps you are right: heterogeneity has to be accepted.