No, it’s called case law. If you’re not a lawyer or educated in the law, you probably shouldn’t act like you know what you’re talking about.
When analyzing whether any governmental agency or body has violated the Establishment Clause (since the First Amendment applies not just to Congress or the federal government, but to the States and state government through the 14th Amendment), courts utilize the Lemon test from Lemon v. Kurtzman, 403 U.S. 602 (1971). A governmental action will not be found to have violated the Establishment Clause if 1) it has a secular purpose, 2) it does not have as its principal or primary effect the advancement or inhibition of religion, and 3) it does not foster an excessive governmental entanglement with religion. The general purpose of the test is determining whether a governmental action or certain governmental speech has either the purpose or the effect of endorsing or disapproving of religion or a particular religion.
If the head of a government-run agency, such as a principal, is making public and official statements endorsing Christianity to his students, that’s probably a violation of the Establishment Clause. If the very same government official (particularly when taking account of his other conduct) actively selects a speaker at a formal graduation ceremony knowing that the student will effectively endorse a religion, that’s probably going to be another violation. A good analogy would be that police can’t simply hire mercenaries to act in their stead to get around the protections of the 4th and 5th amendments when it comes to dealing with members of the public. Similarly, school and governmental officials can’t shield themselves behind students for their planned and purposeful activities when they use those students to accomplish their ends.
