Lazs-
No, you don't get it. The state tells the schools what the required curriculum is. If the school is to receive state money, it must offer and require certain classes, period. Any other curriculum offered is not mandatory in any way. This gives the student (consumer) more choice, but doesn't restrict them. The state sets how many hours are required for a degree, what has to be part of the degree, and what amount of time has to be spent in those classes.
If the state tells a public school it must teach ebonics, you'd better be certain a voucher school would have to, too. Same goes for any other state program.
There is your conundrum, Lazs. Private schools are better because they CAN tell the state to get lost, and this is possible because they don't depend on state money. The minute this changes, the bloom goes off the rose. So, private schools are better, but most people can't afford them. Making them affordable will make them like public schools.