Why not? If I implemented a system, it would probably involve certain things that I wanted students of different age groups to learn (a curriculum). There would probably be people who were in charge of teaching them (teachers). Along the way, we'd measure how well they learned, or how we taught them (tests).
Why is this so preposterous?
1) Kids are mandated by law to attend school, but then when in school, teachers cannot even adequately punish unruly kids because that would violate their civil rights (thanks to a bunch of court decisions in the 70's). That means the worst kids get little discipline, and the good kids get locked in a building for six hours with juvenile tormentors.
2) Schools make less intelligent kids feel like they are inadequate because they are not as good at a narrow range of academic skills. And for what? There are many productive ways to earn a living that require neither algebra, physics, or history.
3) The worst delinquents do not want to be at school. The teachers do not want them at school. They do not get anything out of school because the teachers have no ability to control them. The system is benefiting no one.
4) Teacher pay has absolutely no relation to the quality of their teaching.
5) Districts pay a ton of money for the tools required to equip a vocational school. But those tools already exist in the workplace, and these craft businesses all used to except teenagers at entry level positions where they could learn the ropes for free ( or even get paid).
6) The smart kids who actually do want to learn are usually not allowed to. They are usually beyond the curriculum, yet are forced to go follow the exact curriculum set out by bureaucrats hundreds of miles away.
7) We live in an era where there is far more information in the world than anyone can ever learn, and where most economic value comes from specialization. There is simply no reason to have a centralized curriculum, outside of reading, writing and arithmetic.
8) There is no clear reason to have specialist teachers. Schools could be designed as parental coops. Or as a series of workplace internships. Or as apprenticeships. There are many, many models to use.
9) Why not use older students to teach younger students? It saves money and breeds responsibility.
10) Why segregate by age? Why cut off children from the rest of society in a big box building? Kids always act better when they are trying to impress someone older. Older kids act better when they know younger kids are looking up to them.
11) Despite a tremendous increase in the hours spent in school over the past 90 years, tests of numeracy and vocab among the general public have been flat.
12) Why assume that we need high school. We got through the 19th century just fine without it. What changed?
13) We send kids to college to supposedly educate them, but where the real result is spending 4 years of partying and no responsibilities.
14) The left puts up huge fights against voucher funding for private schools, because they fear that will lead to more class segregation. So instead, many posh suburbs have essentially become expensive private boarding schools where the parents live too. Instead of the different classes living in the same town but going to different schools, they live in entirely different towns altogether.
15) A student has his school paid for for 18 years. But after that he is entirely cut off. Why can't a student take a few years off when he's young and does not appreciate school, and then have the money available when he's older, and realizes he needs to a community college degree to achieve his chosen profession?
16) The school system pretends that it is supposed to raised up the lower classes and increase their earning potential. But in reality, the reason for much of the earning differential between drop outs and graduates is that there are needles barrier to entry laws for many professions. Take away those laws, and lower class students could simply self study and test into the jobs, rather than spending a huge amount on college.
In order for your plan to work, it assumes that either the kid is bright or the parents place a high value on education. Think about this scenario and tell me how you take care of it.
In the meantime, the current system does a good job of providing a baseline education for all.
If parents cannot raise their kids properly, well, you have a major problem. Fortunately, parents evolved to care about their kids more than anyone else, and they are also much closer to the problem than any government. The parents that are so incompetent that they cannot ensure their children have basic economic survival skills are very rare.
In order for your plan to work, it assumes that either the kid is bright or the parents place a high value on education.
What percent of jobs in the economy need more than reading, writing, arithmetic, and apprenticeship? 10%? 15%? In my observations its much lower than people think. And learning the basics was never a problem in the United States. The U.S. had near universal literacy since 1800(1), long before the modern educational complex was created. The baseline requires two or three years to teach max. So how does that justify a compulsory 12-16 year educational track?
In fact, part of the reason that so many parents do not care about their kids academic education, is that the kids academic education does not matter. Neither the kids nor the parent is part of the cognitive elite, so they are never going the game in striving for cognitive elite jobs. The parents are right, the government is wrong. The idea that 100% of the population needs to stars in the academic fields is a lie ( or more politely, marketing).
(1) outside of slaves, who were actively barred from reading
My Dad lost his welding job around when I was starting high school. He took a few different jobs, one of which was cutting brush with a machete for a local private surveyor. He found the surveying work interesting, so he checked out books from the library to re-learn his Trigonometry (and probably a few other things). This allowed him to get a job with the Pennsylvania Dept. of Transportation surveying group, from which he took early retirement a couple of years ago. I think having an initial exposure to Trig in high school allowed him to realize this career change was possible.
So, it is hard to say what knowledge will be useful, or not, over the course of a lifetime.
Anyway, it should definitely be possible to test out of the default classes/curriculum. If one understands what one is ostensibly going to be taught for the year, one is better off spending one's time doing something else.
12) Why assume that we need high school. We got through the 19th century just fine without it. What changed?
The complexity of the world changes. The minimum amount of education required to function well in society increases with it. (In particular, knowledge with basic sciences and technological skills.)
An average person, though not everyone, would need more time to absorb information and skills to prepare for adult life. Schooling might not be the best means to train them, but until an viable alternative is implemented, we still need those extra years.
You can also took at the most technically skilled people from the 18th century - architects, civil engineers, mechanical engineers. Their jobs were just as complex as the modern equivalents. Yet probably half of them entered their profession with no education beyond grade school. They learned on the job.
Schooling might not be the best means to train them, but until an viable alternative is implemented, we still need those extra years.
Schooling does not provide any training at all for 95% of the jobs in the market. Most people learn everything on the job.