Elite private schools have limited capacity and the cost is the major control mechanism. LJCDS already has all the kids they want. They would just increase the cost by whatever the value of the voucher is.
I am a bit surprised that you would argue against Common Core, FLU. Important purpose of math in school is to develop problem-solving skills and common core math is doing that. It is the path that matters, not the number at the end. My 4th-grader can solve quadratic equations, but as long as he cannot explain the solution he is just a well-trained monkey.