Our kids have been in classes that were both heterogeneous and ability grouped in elementary school.
One of DD13's best memories is her third grade year, where her entire class was gifted. The teacher had a squadron of helpful, connected parents (she had FOUR room moms!), a class that was engaged and excited and stimulated by the pace set by their peers, and CRCT scores that were the highest in the history of the school (which was considered a top ten in the state already).
It was a magical year, and the teacher was in tears the last day because the school chose not to continue with it next year because of sniping from other parents.
The flip side? In the heterogeneous classes DD11 would finish her work in five minutes, then spend the rest of the time teaching her friends the material and helping them through it (because she has that kind of temperament).
DD13's experience in the heterogeneous class was a kid who couldn't do the work and exploded with rage regularly, at everyone. He needed help he was not getting, and it was not fair to him or his classmates.
In middle school they're ability grouped for all academic classes except reading (which boggles my mind, but whatever!) and their experiences with their classmates and the curriculum have been pretty good.
They both notice that the girls in their reading classes obsess over boys, looks, weight, and other people's business. The girls in the gifted classes are too engaged with other topics to really focus on the above topics with the same ferocity as the regular kids. It's definitely there; but gossip is not the center of their universe.
