From Libertarian Wiki

Public education is an education system paid for by a community. In the United states the public education system is secular because the first amendment prohibits the establishment of religion. Upholding this secular status involves a restriction of the kinds of speech a school employee is allowed to exercise because as an employee of the state a teacher may not perform an action that is constitutionally prohibited by the state. Students are not held to this standard which is why teacher led prayer is strictly forbidden in schools while student lead prayer is only forbidden where it interferes with school activities(such as out loud during a test); it is therefor a mistake to say that school prayer is outlawed, one that is often made on purpose.