There we get into the concept of “government endorsement of religion” and individual rights.
I firmle believe that, although teachers, at school, cannot endorse religion, a student can, in a speech, laud whatever god he wishes. I believe the constitution protects that for the student for he is not an agent of the state. And if the teacher is on his own time and not acting in official government capacity, he can do the same. And no city or state (or federal) law should stop him, if it is to be considered constitutional.
Just an opinion, of course.
They had that right of free speech until the federal judiciary used an "incorporated" First Amendment to silence their speech.