Montessori advocates for mixed age classes where more advanced help teach the less advanced, as the teaching itself solidifies it in the more advanced student's mind. Not sure if it is valid. But it is something with studies and meta studies that may have been done well or poorly, not just an aesthetic choice. I think Vulcan style training pods driven by AI like khanmigo will end up being better education than the vast majority of students will ever have access to in person. Or consider it the realization of "a young lady's primer" from diamond age.

Montessori does advocate that, but mixed ages is not mixed intelligence.