The MBUSD library catalog for all schools can be found here. For PK students, the procedure for logging in and holding a book is described in great detail below--scroll down three blog posts and you'll find it. That's what you should do to borrow a book from the PK library.
To see what books the PK library has, visit the library catalog, and use the search feature. When you find a book that interests you, click on the number of copies (at right of the title), and you can see which schools have a copy.
A good way to find historical fiction books suitable for use that are in the PK library is to go to the PK library catalog, click on the Catalog tab, click on Resource Lists at the left of the page, and scroll down to PK 5th Historical Fic. Remember the things we've discussed, students! Click on the book's title to see what it is about, if a copy is in, how many pages it is, and what the Reading Level is (the "difficulty" of the text, expressed as grade level). Make a good choice and click the Hold It button. (You have to be logged in to hold a book, so if there is no Hold It button, be sure you are logged in.)
Students from other elementary schools who are in a PK class can check out books from PK's library if they would like, or from their "home" school library if it is currently checking out books, and of course from the public library system.
Students from other schools cannot log in to the PK catalog, so those students cannot use the hold procedure to request PK library books. I'm sorry, it's just a limitation of the system. Students from other schools can request PK library books by emailing me or their teacher. The books need to be picked up from and returned to the red wagon in front of the PK school office during school hours. (It may take me a day or two to have them ready!)
There are many websites and blogs (e.g., Goodreads, Book Riot, Reading Rockets) that have lists of historical fiction books for students in grade 5. Try an internet search such as "middle grade historical fiction" or "historical fiction for grade 5." Obviously I am not endorsing every result that comes up! However, you will soon see there are many excellent lists, and also many titles that turn up on more than one list, so with a little research you should be able to find some good options.
Any questions, please do not hesitate to email me.