I seriously think they do not realize that he is planning to stay home that day. I imagine if I didn't sign a permission slip for a trip at my son's school the teachers would be a little frantic wondering what they will do with him if I expect him to be able to be at school that day but not have permission to attend the trip. YKWIM? I am sure once she tells them he will be home that day they will be fine. No school can be this weird... at least not openly! (or can they???)