I can't recall ever worrying about a classmate opening the door when I was in field service. Maybe that is not too surprising- growing up in a bad area, it was unlikely that parents would allow their kids to get the door when someone knocked unexpectedly. And I have no idea how I would have responded if a classmate had opened the door. But as I recall, we did not get any grief about our religion in school. Most kids just saw it as a kind of weird thing, a curiosity. I never did appreciate how lucky I was.
As for the pledge of allegiance, I had it kind of easy there as well. We (there was usually one or two other JW kids in my home room) either stood outside while the rest of the class made the pledge, or we could sit at our desks or stand quietly with our hands at our sides. To be honest, it was easier to stand outside than to be surrounded by kids when you were explicitly not doing what they were doing. But again, I don't recall getting any shit over it.