Kids in middle schools learn very little. There are studies on this too -- you can skip middle school and lose not very much at all. They're notorious for behavioral problems. It's often a toxic experience.
It's the time when, from an evolutionary psychology perspective, people began helping support families and to have meaning and purpose in life. When I've visited countries when kids do elementary school and then go work the fields, that whole set of behavioral problems and toxicity was avoided. Of course, kids also left school, so I'm not claiming that's a good alternative. But a wealthy nation should be able to provide one:
1) I believe that providing kids with meaningful work starting in middle school would reduce much of that toxicity.
2) I also believe providing kids with work would motivate learning. Right now, kids often ask why they need to know "this," and don't know how to pick majors when they hit college.
To be clear, I don't believe just throwing kids into the grinder, metaphorically speaking, and sending them off to flip burgers at McD's would do any good. Ideally, I'd be thinking of a structured process -- internships and similar where kids have something meaningful to do aligned with their interest. If a 12-year-old is interested in art, they're sent off to do something at an advertising company.
On the other side, when kids leave college, I also wouldn't throw them into a 40-hour (or 70-hour a week) grinder. I'd also try to structure jobs which pay less, but provide for learning and mentorship. Your first few jobs out of college, you should still be taking perhaps 1 class per semester.
As a footnote, I also needed to pay my own way for much of college. My short-term mental/physical health suffered for it, but in the long-term, I'm better off for it. I'm not claiming that's true for everyone (so much of this depends on the specifics of the jobs), but I'm claiming it could be.