There is statistics that just came out that charter school definitely outperform public school everything equal. ( parent status, living condition etc).
Teachers union is a very powerful liberal lobby. They are interested in getting as much money from the gov. as possible.
You don't believe that they are pursuing their liberal political agenda? :-D ( I wonder why they donate millions and millions to the Democratic candidates)
BTW, there are good teacher in public schools.
There are also very bad teachers there who are not "fireable" due to the union protection.