I don't do that, I rarely, rarely leave class without a note. We have to sign a note in the back of a book we have at school, our Diary, and we have to state where we are going, what time we are leaving, what the date is and the teacher that's in out class, has to sign it. That's the only way for us to leave class and I don't make loud obvious noises, unless chatting with friends counts, which I'm sure it wouldn't.
So you teach LostVoice? If so, which classes?