A public high school is holding a religious baccalaureate service. Is that legal?

It is a fundamental principle of Establishment Clause jurisprudence that a public school may not advance, prefer or promote religion. Because it is generally understood that a baccalaureate service is a religious event, a public school may not be involved in the organization or execution of a baccalaureate in any way that would make an objective observer believe that the school is endorsing the event

It is impermissible for a school to financially support, organize, or have direct influence over a baccalaureate service. Below are a list of things to look for in a baccalaureate service that might cause an objective observer to believe that a school is sponsoring the event.

Read more: https://ffrf.org/faq/state-church/item/14024-school-involvement-in-baccalaureate-services