Well, me and 2 good friends sat on a bench at lunchtime and prayed for the whole hour, because a girl had committed suicide the night before (this was about 2 weeks ago) Of course, we got a bunch of odd looks and stares. I counted 10 people asking "what on earth are they doing??" in short whispers. Since then, we've made it a habit to pray openly for as long as we need to at lunch. (It's usually about 10 minutes or so). No one has stopped us yet!
I'm not sure if we are allowed to do this, because I do go to a public school. But then again, I live in Canada, so it might be different than the states.