Directors do use assistants or allow observers (I had an assistant directing gig where primarily, my job was to learn -- however it was after I finished graduate school), but other than the sdc observership thing, in a lot of cases these aren't gigs you're going to find posted on the Internet; it's a through-the-grapevine thing in a world of who-you-know connections.
That being said, at the high school level, while, yeah, it would be mega impressive, I wouldn't really worry about landing something like that. Far be it from any of us to stop you trying, but I wouldn't make it your primary goal. The advice to assist a director local to you is good advice -- it doesn't have to be Broadway to be great experience. Do a lot at a reasonable level. Take on lots of responsibility where you are and don't worry about The Name. Start now with things like that and you'll work your way up to something bigger as you get farther along.
And additionally: colleges also like proper spelling.
A work of art is an invitation to love.