How would one teach atheism? Its not as if its a discipline and it has no rituals to classify it as a religion. You cannot be indoctrinated as a result. Saying the class teaches atheism must be a ploy deployed in words to make it sound terrible. Atheism I'd the RESULT of skepticism and rationality, both of Those you Could teach. However not atheism itself. That'd just as bad as teaching creationism. You smash an answer to the kids faced without letting them see the problem worked out. I sure hope that's what they mean to teach and not just "there are no gods because there is no proof" logic loops.
"He who so forgets history is doomed to repeat it." - Churchill