Quit school (college level, but where I am it’s just another part of school) when I could (I had the right age to make it my business), without ever discussing the matter. Just came home and said I quit school.

Edit: Oh damn you wanted a reason. School was hell for me, I hated everything about it. I had spent about 6 months exclusively doing the classes I was interested in and nobody even took notice. I figured they weren’t gonna kick me out at that point, so I quit.