Religion CAN be taught in public schools and IS in the good ones. As Damo said, often in middle school social studies-ancient history. I've said before within that we cover polytheism, mythology, Judaism, Christianity, Islam, Hinduism, Islam, and Buddhism.
While I happen to teach in parochial school, my son went to public middle school, same text and same approach by the teacher. Catholicism is not a literal bible based religion, so we have few problems with our science curriculum, (though the science teacher is a 'born again' evangelical and tried to put ID into program a few years back, the kids told me, I told the principal, and the pastor 'advised him about inappropriateness.') ID/creationism is addressed in religion classes, along with the Churches position on evolution/science and the purposed of Bible study.
http://www.ed.gov/Speeches/04-1995/prayer.html#4
http://www.religioustolerance.org/ps_pray.htm