Oh, for the love of . . . :rolleyes:

You can pray in school. You can pray to your heart's content.
You can run up and down the halls, chanting the Lord's Prayer if you want to, as long as you don't interrupt classes . . .

What I think you're clumsily trying to illustrate is that the schools cannot endorse group prayer. The schools cannot allow (or force) someone to get on the PA every morning, and lead everyone in a rousing rendition of "Hallelujah, Amen!"
That's where the courts have stepped in, I believe.

But no one is going to bumrush Johnny on the playground and hold him for the authorities if he's praying to himself . . .

As long as you don't disturb studies or classes, pray all you want . . .

It's a t-shirt. If he is even coming to school sober, without a weapon, then let him take his seat and teach him something.
Big fuckin' whoop . . .