It's "separaton of church and state" that keeps religion out of public schools. Although, not entirely. It's ok to teach comparative religion in public school.
And thank God we have the doctrine of separation (whether genuinely Constitutional or not). Else you *know* that the religion of choice of many educrats would be Buddhism or Islam, anything but Christianity, if religion was allowed to be endorsed in public schools.
After Mark Steyn's recent article on demography, where he makes a compelling case that western democracies will be overrun by Islamic masses in a few short decades, it's even more important that we promote a secular public life, and leave religion to strictly private affairs. Otherwise it's pretty obvious that our great-great-grandchildren (if they're ever actually born) will live in an Islamic world.