Alexander and the Terrible, Horrible, No Good, Very Bad Day
I think this would be a good book to read in the first and second grade. It shows a young kid who may be going through some of the same things they are. For example, Alexander's best friend tell him he is no longer his best friend, but his THIRD best friend. This is something that happens often in elementary school. I think this book would bring a little humor to the classroom while still showing the students that not every day is going to be perfect. This could also be a good opportunity for a writing prompt about the worst day they have ever had.
