Except there's no reason to believe extremist schools should grow significantly. Most people aren't extremists (pretty much by definition). In fact, good schools are a usual top tier concern when looking at housing. Your worry about fly-by-night schools extracting profits and fleeing is also not particularly hard to solve: hold them liable for damages/a return of n years of voucher funds if the school fails to meet standards and require them to carry insurance or post a bond to prove they can meet their liability. High performing schools or new schools associated to people/organizations with a previous success record will have cheap premiums. Dodgy schools will have expensive premiums or will be uninsurable. Your worry about special ed is also not that complex: give higher funds for those kids to offset their higher cost.