Year old thread, but I'll bite.
What we learned in high school isn't necessarily what is now being taught in high school. Without high school, I'd be historically illiterate. It would have never dawned on me that starting a new country teaches anything about life. It would never dawned on me that making a cotton gin or an engine would change society. It never would have dawned on me that maybe genocide is a bad thing, particularly given my mind would have been set on only my ethnic background is the "proper" mindset. Of course, we were just getting to the point of going from thinking for yourself to thinking what teachers dubbed as the proper mindset back when I was in high school, so now that it is teaching the proper mindset, history is out. You can't really teach that life matters anymore, except for the proper PC lives, so heaven forbid, they teach that there was good and bad in setting up a new country devoid of a state religion or that religion has benefits as well as negatives. Religion-bad is taught now.
And, as much as I still hate it, try calculating how much was removed from your paycheck for taxes without ever taking algebra, and try figuring how many tiles is needed to put in a new kitchen floor without geometry.
Without high school, I would have never learned how to write an essay or an article. I would have never been taught how to footnote, even if now I have very few memories of how to footnote. At least I learned how to gather material to learn whatever I wanted in high school.
Without high school, I would never have learned there are choices after high school. In my case, I would have been forced into being a secretary, or, worse yet, just go to college to find meself a Man to take care of little ole me all my life.
Funny thing, I did choose college, did graduate, never even looked for a Man, and ended up getting married and then doing office administration and bookkeeping, so life didn't change that drastically, except it wasn't forced on me.
We teach kids what they need to know in the time and space we think it should take them to learn it. John Quincy Adams already had the diplomatic experience to be the ambassador to the Netherlands when he was 14. Ben Franklin ran away from his brother's apprenticeship and landed in Philadelphia when he was 17. Franz Liszt wrote his first musical composition at 4. And S.E. Hinton published her first novel while still in high school.
Nowadays, we're teaching people they're still too young to get married at 30. And, they believe that. I think schooling should be reconsidered, but never from the viewpoint of people who have made it their career to educate the asses. That's conflict of interest. Then again, do I really want it decided by those who thought high school was useless?