Where we live, legal dropout age is 16...where I grew up, it's 18 - although I believe it was 17 when I left (not entirely sure). I left when I was 15 and wasn't all that concerned with legalities.
When I left, I'd already been skipping heavily for four years...I just barely made it through my freshman year and then a few weeks into my sophomore year, I made a dash for it and never went back. I hated my school, but it was honestly more about getting out of my house and away from my parents at that point. I had a sucky home life, was doing awful in school, I'd skip, I'd get suspended, I'd get expelled for not showing up (and then my father would pay the smarmy private school folks off until they reversed the expulsion), I'd show up just to take the tests in order to pass the class (barely), I hated the students and the teachers and they hated me, I preferred running (as in, hop a train and get out of town...not cross country school sport/activity) to showing up for school...the more I got in trouble, the more my sorry a*s felt like the world was against me, the more I wanted to leave...I stopped caring and so I left. I don't have a GED...when I got my life back on track a little bit, I began to push myself through college and an online schooling curriculum, simultaneously...and then tested out of high school. There was nothing the school could have done...and by that point, there was nothing anyone could have done...my parents could have turned it around and been the best parents in the world, but it still would have been too late...I had to figure sh*t out on my own.
A lot of the people I knew who dropped out were teenage junkies and alcoholics just like me...a lot of us came from abusive homes....a lot of us felt like school was stifling...a lot of us felt like we'd be better off on our own without people telling us what to do...a lot of us just didn't care.
If my 16 year old comes to me and tells me he wants to drop out of high school, I'll ask him what his plan after that is...and it better be a good one. At that point, we'll hopefully still be homeschooling and my hopes in doing that is that they can learn as they want to learn...if he feels in control of it all, hopefully it won't be something he feels stifled by. If he wants to quit school, leave home, hop trains, and do drugs like his ol' lady...can't say I'd support it...but hopefully I won't raise my kids to be dumba*ses.