As a reluctant educator, I have a rather jaundiced opinion of the purpose and feasibility of education.

School learning is a poor fit for a variable portion of the population.  A lot of kids don't want to be in school, they don't want to listen in class, and they don't want to do homework.  I didn't want to be in school, listen in class, or do homework when I was young, so I understand entirely.  I think the proportion of kids who don't want to be in school and who resist the whole process has also been rising in recent generations, as it's become less of a route upwards and more of a meaningless series of hoops that guarantee nothing.  Why work hard towards a pointless goal?

It's also pretty useless for much other than professions whose basic skills are dependent on school learning - historian, for example.

The whole system should be scrapped.  Elementary-age kids should have various fun organized activities with other people their age, some of which might be educational.  They are pretty easy to manage, and don't resent adult guidance, and need to learn how to be social.

People from 12-15 are pretty much useless from an educational standpoint.  Too much important physical and social development stuff is going on.  Sure, a tiny braniac minority can learn a lot during this age, but even for them it's not necessarily the best way to use their time.  Put them into a supervised work service program.  Go dig ditches in the forest and live in barracks, and be stupid teenagers for a few years.

Then give people a choice.  Some can go to school and learn stuff, others can live as adults and build work skills.  If something needs to be learned later on, learn it later on, once the need is clear and the motivation is present.  Really, we don't need all that many people with serious professional skills and abilities anyway - the idea that everyone will have an academic or professional job is just silly, and lots of jobs can be learned to a very high level by on-the-job learning.

Obviously, this will never work so long as going to the right school and studying the right thing is a clear class marker.  An educational system better matched to human development and ability will only really be possible once education is no longer tied to class status and achievement, and that will really only be possible in a classless society.  So good luck with that.