We don't go to every classroom, that would be hard to do because we have around 7 classes per grade level, plus VPK and ESE rooms. So, I put a sign up sheet in the mailroom about a week before we go caroling and allow teachers to sign up for a time. I know that most classrooms have a packed schedule of holiday activites, so this gives teachers the option.
Here is the sign-up sheet I use:
Some years I have had a majority of teachers sign-up. When that happens I ask for chorus parents to volunteer to guide a group around the school. I then split the 5th graders into two groups and we divide and conquer.
If you would like this form, you can request it in the Freebie section of my blog.