The commie piggies are violating the First Amendment rights of these students. The First Amendment is about Religious Freedom. Those who believe that it’s about Freedom from Religion have obviously been doing way too many recreational drugs.
It's about both freedom from (state imposed) religion and freedom of religion.
It's not that hard to read:
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof...
IOW, no FEDERALLY sponsored or supported church" and no banning of any other church/religion, or of religious expression.
In this case the state (school system) is banning religious expression.