They can't prohibit the practice. Duh. But they don't have to allow it in the middle of a public high school's graduation ceremony. This little idiot can have all the altar calls she wants on her own time and in her own place. In a public place and on a public ceremony, this is out of bounds.
SD
I refuse to worship at your church/temple/synagogue, to your god(s), in your manner, and there's not a damned thing you can do about it because I live in America.