Sideways Stories From Wayside School by Louis Sachar

I love this series, including the arithmetic books.  When I read them to my students, I always have a discussion about how it may be okay for students at that school to talk that way or to do those things because they are not at our school.  I want to make sure they know it is a fictional story because I don't want them to pick up some of the bad habits that the students display in this book.  The book is so obviously fiction, it is easy to help them see the distinction.  It is such a fun series to read.  The first one is my absolute favorite.