There were studies made in India that showed otherwise. Without segregation the teachers were teaching to the level of the smartest students in the class, so the slower students were being left behind and became unmotivated. With segregation, the teachers were still teaching to the level of the smarter students in the class, but that level was much closer to the level of the slower students so they could catch up.

Keep in mind the actual reality of the situation might be different in each country, so it's not like one set of studies was necessarily wrong. Maybe teachers in the US teach to the level of the average student, so the results would be different there.

The assumption there is that the ordering of the students by performance is stationary, particularly in the first few years. Regardless of personal situation.

If a child catches a flu at the wrong moment, it will get stuck way below its level for all its career.

Khanacademy data has shown that students in a math class will progress at different speeds at different times and that their "ranking" can invert multiple times over a school year or beyond. It's not exactly the same, but their system makes sure students don't stay stuck.

That's really interesting. Do you perchance have something that might help me find those studies?

I found them on a book called "Poor Economics". The authors also teach an online class on development economics where among other things they talk about education in poor countries.

https://www.edx.org/node/92491

Is there any evidence that segregation is actually better for more intelligent students? And to what degree at what cost?

If you have a class full of "good" students, it's a lot easier to work and teach, than with a class where 1/3 is almost illiterate, 1/3 doesn't care at all, and only 1/3 actually wants to learn.

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.

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

I'd imagine the only reason it isn't so obvious as to need no justification is because children self-segregate by intelligence in schools anyway.

I went to a highscool where there were about 20-30 International Baccalaureate Diploma candidates and about 1200 students in regular, honors, and a handful of AP classes. My junior and senior year I was in all IB classes, but freshman and junior year I had to take a handful of the regular, honors, and an AP class and they were all absurdly slow and easy to be successful in to the point that I would entirely disengage. Had I not been in such a rigorous program I think I would have almost certainly made worse choices in relation to my education and life outside of school.