Should the Declaration of Independence be taught in public schools? Of course. So should the history of Christianity, Judaism, Islam, and other religions. None of that constitutes government endorsement of religion, whereas teachers leading students in a pledge which asserts monotheism does.
"whereas teachers leading students in a pledge which asserts monotheism does. "
Monotheism isn't a "Religion" only a description of types of religions(plural) that believe in one God.