Heh, we happened to get midterms on April 1. One of the top guys in the school with an average of like 95+ received a midterm with like failing grades, but it had his name on it and all his classes. He went to the office to straighten it out, and the secretary just looked up and said, "April Fool's!", and handed him his real report. He just stood there for a minute. Good times, good times.
That happened to us, but they took the most teachers pet girl, who always followed the rules, and then they started talking to her about the dresscode. The Vice-principal made her lift up her arms, and then she was talking about how that was a violation of the dresscode. She said, "First, we will start out with monthly detentions, then some referrals, and if you keep dressing like that, we will eventually make it zero tolerance and have you suspended" and the girl started to cry, and then she said: "April Fools". >_> Plus they had a hidden camera in the office so they broadcasted it to everyone on friday in the morning over the tv.