Power
Um...not a lot.
Actually, hold that thought.
You'll have some power in the classroom—where you get to be the (hopefully friendly and understanding) dictator. There are also opportunities for leadership positions within the school. No, you can't just become the principal or football coach, but there's always the chance you may become the special education department head. So there's a little power in that.
But budget cuts and the ever-changing state educational policies can be frustrating. You're more of a pawn in the big game of educational chess.
It can be hard not to feel a little smaller than everyone else. (Source)
You will have a chance to air your grievances (and suggestions), which may lead to change. If a teacher is persistent enough (extremely persistent) when working with the administration and state education lawmakers, their ideas may even spark change.
Just to reiterate though, your main power will be in the classroom. You'll have the power to make a difference in the lives of every student that enters. It's cliché and it sounds like the logline to a knock off of Freedom Writers, but it's one of the reasons why special education teachers become teachers. So take solace in the fact that you're one of the good people out there, using your power for good.