[adrianN]

I attended a talk about this topic that used the PISA dataset to show this (well it showed that in countries with segregated schools the performance of students had fatter tails on both sides of the mean iirc). I think the data should be available online somewhere.

[ghaff]

Yes. It appears that the more stratified educational systems are, the more variance in outcomes there is. e.g. [1] Which makes intuitive sense. While there's an intellectual argument for everyone benefiting from diversity of a student body, I'm not sure I'd expect to see a benefit in strictly measurable educational outcomes at least.

And it's fairly obvious some of the ways that motivated and high achievement students could benefit from more customized and self-paced study while it's also obvious why a group of students lumped together as low achievers will do less well.

[1] https://www.oecd.org/pisa/keyfindings/Vol4Ch2.pdf