"Participation is voluntary, so I’m assuming a motivated group of teachers."

Just to be on the safe side, I would expect at least one outspoken "atheist" who comes along purely to sneer. If s/he doesn't appear, great, but it's better to be prepared.

I would suggest visits to people like Vicki Davis's (Cool Cat Teacher) and Jeff Utecht's (Thinking stick) blogs to show what other high school teachers are doing.