A primary school teacher played a prank on the whole of year 6 just after their SATs had finished by telling them they had another exam the next day. They actually assembled the kids and "explained" why they had not told them about it before! Then the joke was revealed and the kids had a post-SATs treat.
I think this is a bit mean and not very funny in what could have been a stressful week for some children. AIBU?