Being successful doesn't have to mean having perfect grades. It's a combination of being a leader, participating in a couple extracurricular activities, having a great attitude and doing your best....
idk... but look at Bill Gates. He was a drop out and he's doin fine!
That depends on wich country you live in.
Because high school is probably too hard for them. High school makes them so fed up that they had it with school. So no returning back for them.