I'm student teaching right now, and the pledge is said every Monday morning over the intercom. I usually join in if a student does (they don't always), but I never say "under god." Even as a Christian, I objected to "under God," going so far as to write my first college-level persuasive essay on the subject. As a child, my biggest objection was the fact that it's a pledge of allegiance to a FLAG, and "the republic" is sort of an afterthought.
I won't force any students to say it, or to even be quiet during it, but if I see a student who's participating, I'll join in.