Hahaha. This was hillarious.
I loved the one hidden behind the callendar. What schools are we talking about?
It made me remember my HS. We made an experiment when we started and proved that for 5 years noone cleaned the windows of any classroom. We had left some messages written and 5 years later they were still there. Had I known Lovecraft then I might have concocted something far more sinister.
For our graduation speech the principal wanted me to include a note thanking the janitorial team, as a courtesy. Hell no!