Does it though? I feel like the classes in which I had the most camaraderie with others were the mixed-age ones (math, grouped by ability, AP classes, and swim,

Does it though? I feel like the classes in which I had the most camaraderie with others were the mixed-age ones (math, grouped by ability, AP classes, and swim, a mixed bag). Likewise, the significant majority of my friends were first in grades above, and then below me. And it's not as if people of the same age can't bully each other. Even with younger children I don't think it's as much of an issue for bullying. In fact, if such mentorship programs are voluntary, I'd wager there would be less of a problem; you'd be surprised at how empathic children can be when placed in an older/younger pair. There's also an self-evident dynamic of power there - it's when children are expected to act as peers that squabbles for power most frequently manifest as bullying.