Right well, I think it depends upon your situation to be honest.
I had to drop out to move on. I was a junior, top ten, very involved in sports and the various geek clubs. But I was also miserable. I wanted to leave early, but the school system said they refused to graduate me because I did not have 4 years of P.E. and History. That's right, you heard me. I had enough math, Science and English, but not enough P.E. to leave.
So I dropped out.
But the difference is I went directly to college. It turns out most private colleges don't really require a high school diploma, they only require decent grades and a good SAT or ACT score.
I still say it was the best decision for me at the time. I think when it comes down to it, you have to look at what is ultimately best for you. If staying in school isn't really going to get you to college, get out while you can, learn a trade and move on.
If you really want to do something that requires going to college, get enough out of your high school that you can jump to college sooner rather than later.
I'm one of those people who really doesn't think the institution of school is all that great. I went all the way through to get my Masters, and yes, my job has been nice. But I know people who left high school, got jobs right out, and now make very decent livings as well. I feel college is a way for people to feel like they are better than all the unwashed masses. Just because I read Plato in college doesn't make me better than the guy who changes my oil and dropped out of high school. Plato can't fucking change my oil.
I believe college is just a subtle way to reinforce the caste system. This isn't a particularly popular belief among my peers, but they also consider themselves above socializing with the "lower class" as well. College is the way out, but not because it makes you smarter (knowledge does not = intelligence. Knowledge cures ignorance only.) or a better person. It's the way out because society has deemed it so. But I digress.
Decide what you need to make you happy in the long run. If you think you will need a white collar job to be happy, then by all means, stay in school. But if you think you can be just as happy working blue collar, go for it.
If you have supportive parents, you can always go back to school. Both my parents dropped out of high school, and they had a family by the time they went to college. It was hard for them, really hard, but even that can be done.