I know many children are preparing to go back to school or perhaps starting school for the first time! If you are starting at a new Montessori school chances are you have already completed an observation and your children may have already visited their classrooms.
My children started in the Montessori classroom (Cycle One) when they were around three years old. When I found Jack Goes To Montessori School, I was thrilled. While it's not an official back-to-school or starting school book, I think it's perfect for reading at this time of year. Many books about schools just don't fit with the Montessori philosophy or don't depict Montessori classrooms. It's why I love this book; it's the only picture book I have found that features a Montessori classroom with materials and activities the children will be(come) familiar with. If your child hasn't started school yet they might not be familiar with the materials but after a week or so I am sure the will start to make some connections.
If you have completed your observations at your school and still have questions or simply want to know more about Montessori schooling, there are a few books that I would recommend. I believe Montessori In The Classroom: A Teacher's Account of How Children Really Learn was written for Montessori teachers, however, as I parent I found it insightful. It is more conversational and more of a personal recount than other books, but I like this. Montessori Madness was written with parents in mind. It is more of an argument for Montessori (pushing the point at times) but still really useful in finding out how children in Montessori classrooms behave and how they learn.
I recommended having a look at your school's parent library (hopefully, they will have one that is well stocked) for The Montessori Children's House: An Introduction, What is Montessori Elementary (for students moving into elementary) and A Parent's Guide to the Montessori Classroom. These are brief but can be helpful for those completely new to this environment. When Caspar first started school I was at the parent library weekly, it is a fantastic resource!
Does your school have a parent library? If not, you could ask your child's teachers, they may be able to make some good recommendations or find some books available for loan.
Edited to add: I really love this book called Oscar's Lunchbox, which could also be useful going back to school if your child has food intolerances. It is a story about Oscar (who has food intolerances) and his lunch box looks a little different to others. My children don't have any food issues but I like the story as it is really about acceptance and eating what is good for your body - everyone's lunch box looks a little different!