I don't think complete segregation is the answer, but within a given school, I believe there can be more malleability. In general, the idea of which class you e

I don't think complete segregation is the answer, but within a given school, I believe there can be more malleability. In general, the idea of which class you end up in being more skill based than age based. And not everyone is better at every subject. Having it per subject allows someone to go further in math even if they struggle with some other subject.