Slight devils advocate. Is everyone happier with mandatory schooling for longer? It isn't that we shouldn't give everyone the chance to learn, but maybe some people really would be happier dropping out at 14 and just getting a job. Being at school where all you do is fail does not make for a good life experience!
I think the answer is probably that we don't want parents pulling kids out of school early just to earn money for the family? So legally requiring they stay at school longer protects.
14-year-olds are likely not equipped to make such a decision. If all you're doing at school is failing, then the school itself should provide better support mechanisms.
Better support to what end? Walking out of school age 16 with 4 GCSE passes is not much of an improvement on 2, and maybe we should accept that there exist people who cannot via standard schooling do better than that? Maybe those two additional years of special measures is not better than a couple of years learning on a job?
Unless your claim is that with sufficient support everyone can leave school at 16 with good grades, which is simply not a school of thought I ascribe to.
My grandfather went to school until he was 14, but he was also highly literate, had a keen technical insight, and was generally fairly smart.
He wasn't unhappy in life, or the way his career as a factory worker turned out. At least, as near as I can determine those kind of things: he was an old-fashioned kind of man who didn't have a heart to heart with his grandchildren. He never ate pizza in his life, and refused to eat it when I offered to take him out to try it.
But at the same time I've always felt he could have achieved much more if he continued school. The reason he didn't was because his family was poor and another child working was needed to put bread on the table. A big reason this mandatory schooling exists is for these kind of reasons.
That being said, I do think there's too much emphasis on degrees; not having a college degree is almost something you're embarrassed of. My brother did basically a useless "animal care" study because he felt like he had to do A study (note: it's not a useless education, but there are tons of people doing it and very few jobs, almost no-one who graduates gets a job in that field and the impression I had from his friends is that it's mostly the kind of thing people do when they don't know what else to do).
I think the answer is probably that we don't want parents pulling kids out of school early just to earn money for the family? So legally requiring they stay at school longer protects.
Just a thought