Charter schools are choked by unions?
Nope. This is why charter schools succeed in many difficult areas. The unions dictate the terms of education - 100%. Who can teach, how long they can teach, what qualifications are necessary, how many students in a class, what kind of students can be in a class(think ELA), what materials are acceptable, who can teach what, who can coach, who gets paid what, etc etc. I could go on and on.
The biggy in this is that if a charter school is failing; it gets shut down. Good luck shutting down a conventional public school. Union would never allow it.