If the valedictorian were Muslim at my child's school, I sure as hell wouldn't want to be hearing "praise Allah" during his speech. I doubt any of you would either.
The point isn't whether I want to hear it or not ... the point is that the First Amendment (prior to the pc police taking control) guarantees the right to say it.
What you "want to hear" is irrelevant in a constitutional republic.
I wouldn't WANT to hear any mention of Allah at a valedictory speech, and I would hate it, but if the speaker mentioned it, that would be his right. That's the beauty of this country -- at least it used to be -- a person could say anything with little fear of being condemned.
Basically, if you want to worship Satan, knock yourself out. Just don't tell me whom/how I can worship. The problem is, everyone has rights except the Christians.