how many students graduate high school outside of the specified state-mandated kindergarten start date of their age cohort? Maybe a few percent at most? There may be some mixture of ages in higher grades, but mostly students are stuck in a group of students who are within one year of their age... regardless of intellectual level. Yes -- it's possible in most schools to move out of that system for particular students, but it is considered abnormal (and thus introduces excessive social problems often because it is considered so abnormal).
the ages is the simplest net to catch the largest group for education. Kids will have similar education , maturity, and age related factors that make it easier for educators and the students to learn. It is not perfect and if there is a better way then by all means lets hear it. The small percentage is by definition abnormal so it is reasonable to assume that they are going to have other social problems by being abnormal in this regard (I am not advocating for it but if you have a better idea to account for the 1%). Kids are not nice and are not nice to their youngers. The age groups, while not perfect, does protect the youngest. Not every kid is a special little snow flake that should advance to 12th grade by 12. It is rare and the stats (I don't have them but I would agree with you that is very substantial) reflect it.
Note that these are precisely the same claims that were made when white and black schools were deliberately segregated. Segregation is almost always justified as being helpful to the those who are forced to be segregated -- blacks were considered inferior, and thus obviously it would be easier on them and on their teachers to separate them out.
But your missing the point that in special cases those age limits can be ignored. What special cases would racial segregation be ignored? Calling those age groups segregation is disingenuous. The ages are not as cut and dry as racial segregation and did not have the same consequences when ignored.
Our rather rigid age segregation in most public schools results in a lot of harm, in my opinion. Look at studies, for example, on students who are born in spring vs. fall. Just because students start kindergarten at roughly 5.5 years instead of roughly 5 years often makes a large developmental difference in outcomes, even as late as high school. Then look at the outliers and see how they are affected. Age segregation may be the "best" system of segregation for educational purposes, but I think the evidence is far from as conclusive as you act.
Nothing is perfect. But name a different system that can account for the majority of kids that protect the youth, account for maturity, education, intelligence (for the most part), interests, etc... If we can identify areas of improvement then by all means lets do so and try something. What can we do to account for fall DOBs?
Yes, you are right. You didn't say that. I was not implying you directly said those exact words. My statements were more of my opinion on general of sex segregation. Read 'you' as a general in that statement'
When you say: "the argument that the studies I mentioned make is basically that girls often mature a little faster and could benefit from being separated from a bunch of disruptive male idiots who are still too immature to allow a place for the wisdom of their female counterparts in their (segregated) age cohort."
It sounds like the scientific racism before Brown v Board of Education. I am not going to deny the validity of those studies or whether they are right or not. But In the real world, men and women have to work together. They need to learn that somewhere and at early ages. I do not think women and girls need to be coddled and have special treatment to be successful. If that were the case why are so many successful today? Women make up the majority of college enrollment and college graduates but they still need special treatment?
If you do give them special treatment based on their feelings how far into adulthood are you willing to coddle them? We coddle students in college from scary ideas, might as well segregate the work place too from all those potential rapists and murderers.