I think it's fine to let students pray silently and privately. Same with letting Jewish and Muslim students pray, wear religious apparel, and letting any other religions practice in whatever way that doesn't affect others. But as soon as a teacher tries to convert my kids, or another student tells them they're going to be tortured for eternity for worshiping the Gods how we see fit, there's a problem and said teachers and students need to be removed. In short, tolerate anyone but the intolerant.