If college, he goes to a combination senior high/community college for three years (grades 11, 12, and college freshman) where he studies his advanced math, science, etc. At the end of "junior college", if he has good grades he can apply for a regular college to get his bachelors.
Which means if a kid mistakenly passes on the college route around age 15, it’s incredibly difficult for him or her to catch up later. What you describe is much more the European system, which IMO reduces social mobility.
I agree there are real problems with our current, bloated and largely ineffective system, but in the modern world there’s no reason not to enforce some standard academic rigor through high school.
Here in Southwestern PA, we actually have what you are describing. Starting in 11th grade the kids can go to technical schools. However, not all kids know at that age what they want to do. Also, there is such a stigma about the trades that many kids who should be going to one of those technical schools don’t because they are “supposed” to go to college. Even though they may not have the aptitude for it. They may have the aptitude for the trade school but don’t take advantage of it.
Anyone who can pass the GED or similar private exam should be given an official high school diploma from their local socialist K-12 school district. It shouldn't matter if the child is aged 20 or 5. They should then be able to move directly into college or trade school. ( By the way, they shouldn't get a diploma unless they do pass the GED.)
Having this diploma opens up many opportunities for scholarships and the military that would be denied otherwise. Unfortunately, many states forbid students younger than a set age ( 16 or 18) from taking this exam.
Next,....Charles Murray is right. We need qualifying exams and we should dump most B.A. degrees. The qualifying exams should start in kindergarten and continue through graduate school. If a child masters the basic phonic sounds, or his addition facts, he should be immediately moved to the next level. It is insanity that he should be held behind while the rest of the class catches up.
The Khan Academy is blazing the way in on-line education. If the producers of high quality education content, coupled with certifiable testing, and accepted advertising they could become as rich as Mark Zucherman!
Finally....Every course offered by a state owned and run K-12 school or college should be ON-LINE and FREE to any citizen in the state. Hey! Their taxes paid for it why should it be hidden from them. ( Uh? ...Maybe they hide it because it is grounded in Marxist dialectics and they don't want the taxpayers to know they are paying for the overthrow of our nation? )
By the way, my homeschooled kids were in college by the ages of 13, 12, and 13. Two finished B.S. degrees in math by age 18. One earned a masters in math at 20. All finished all general college courses and Calculus III by age 15. The oldest finished a masters in accounting at the normal age for his generation but also was an internationally and national ranked athlete, traveled the world representing the U.S., worked for a few years for our church in Eastern Europe, and is completely fluent in Russian. ( Surprisingly his firm has a Russian companies and many Russian clients in its practice and he is often called upon to translate.)
One more thing: In June every government K-12 teacher should be required to take the GED. If they fail ( and most would fail the math section) they should be fired. Also, all government teachers should be required to take and pass Calculus I for science and math majors with no separate classes for them! They should sit in the **same** classes ( shoulder to shoulder) with the math and science majors. It might help guarantee that government teachers have a high enough IQ to be in a classroom and it might eliminate a lot of the math phobia they bring into the classroom.