We have the same issues in The Netherlands, with a slowly growing number of islamic schools (slowly because most Dutch muslim parents want their kids to go to regular public schools). I guess it is the same in the U.S. and other counties with freedom of religion plus huge latitude for religious schools. Maybe we need some new approach to religious education, but meanwhile we had better keep a check on curriculum of any such schools (and pull the Saudi or Pakistani rug from under a lot of them).