There was a terrible mistake. Wayside School was supposed to have been built with 30 classrooms all next to each other in a row. Instead it was built with the classrooms all on top of each other. That may be why all kinds of strange stuff happens, especially on the 13th floor.
There are 29 kids in Mrs Jewls' class and this book is about all of them. There is Todd, who is in trouble every day, and Paul whose life is saved by Leslie's pigtails, as well as all the others who help turn a day at Wayside School into one madcap adventure after another.
All the kids at Wayside had to spend 243 days at horrible schools while Wayside was closed to get rid of an infestation of cows! Now they're back and the fun begins on every floor. Miss Mush has prepared liver in purple sauce, and it is pet day on the 30th floor and there is a substitute teacher.