I don't know that I really understand what you are trying to say. Simultaneously, I feel like the answer to the question is probably "It's far worse than you think."

You take, say, 30 kids who happen live in the same area and are born within a particular year and shove them together in a class and they are all being shaped by the same teacher, the same curriculum, the same school system, their parents may know each other or may not etc.

I think you are likely attributing overly much to the children per se and not to the forces shaping a group of children. And I think we have done a lot of harm to how humans think about age differences generally. I feel like as a society we have an excess of baggage concerning dating someone of a different age, as just one example.

Yah I think there’s something to that. There’s this age delta in dating that’s a huge exaggerated deal if someone dates another a year or two older/younger in age cohort schools. There’s almost this disbelief and shock from the peers when they witnessed this narrow age gap being crossed. I used to always attribute the shock to the larger percent differences in age that are calculated in the younger years where a year relative to 10 or 14 is a much larger percentage of one’s age than at 26 or 35 and beyond. Come to think about it yah what was that shock all about and I think I agree that it probably has carried over in weird baggage into the adult age ranges. There’s like a weird mental adjustment upon first finding out about age differences in a given couple from split second shock and disbelief to like “oh yah that’s not that far apart anymore”. The problem with the age cohort model is that all people are assumed to develop at the same rate uniformly. That’s probably not true.

Same could be said about social distortions that manifest in the modern toxic public/private school environment. Different people weight the pros and cons differently. Also what has worked in the past for public school may not be true now when it is highly politicized.