In my experience as a student in middle school and high school there was no such thing as a classroom library. Our classrooms were often used by multiple teachers so there was little in the room besides chairs, desks and a white board, maybe a poster or two. If we had books it was a textbook or the class novel we were studying and being tested on. (Granted, there was no internet, either, this was a long time ago.) I read recreationally in phases as a kid, but it was school texts that were seen as the "important" ones. There are so many negative consequences to this way of doing things--limited viewpoints are learned and validated, reading is seen as a unique-to-school task instead of a useful-to-many-aspects-of-life task, and many kids are turned off the idea of reading because they don't like the books they are forced to read at school.
Now classroom libraries are much more common, though perhaps more in the younger grades. School libraries and librarians are in limbo or non-existent in many districts, but even if a school has a good library and a librarian (as schools should!) the classroom library remains valuable as a way to promote literacy, exploration, and community. My classroom library helps me get to know my students and their interests, helps start conversations between students, and makes access to books easy for every student. It helps even the playing field of who has books at home and who doesn’t, and allows reluctant readers to take a look at variety of books without the time pressure of a library visit and a check out deadline. The more you can get kids talking about texts and seeing them as part of their everyday lives, the better. Books and other texts are more likely to be seen as part of real life, useful and adaptable to many moods, questions, and purposes. This is what I hope texts will be for my students for rest of their lives, and it is important that they experience them this way. (See the work of Teri Lesage and Donalyn Miller for some great literacy challenge and inspiration.)
As a new-ish teacher I am still growing my classroom library. I have worked at two different schools so far and neither had a clear budget for this purpose. In my first school a relative of a coworker generously donated funds for us to buy a selection of books. In my second school I had a small starting budget, did a Donors Choose campaign, and created a fundraising magazine project to build our library. I’ve also let friends and family know I’d appreciate books they are no longer using and I keep my eye on little free libraries when I’m out walking my dog. Thrift stores and charity shops can be good sources as well. And, honestly, I spend a lot of my own money on books, too. Overall I try to be picky and not just take in books for the sake of books. I think about who is in my classroom and what their interests are, and I think about what gaps there are in terms of genre and representation. I have books, magazines, a growing zine collection, and I hope to add a greater variety of informational texts (maybe related to tech, arts/crafts, building things, etc.) soon. (Here's a helpful post from Pernille Ripp on evaluating your classroom selection.)
I use an informal checkout system, usually a clipboard with a sheet for each period. Students record their name, the title and the date of checkout. I assign one or two students each class to check up on the list once a week--though my implementation of this system could be improved. On Pernille's Passionate Readers facebook group, a member recently mentioned giving a jolly rancher for every book returned at the end of the year as a good way to get books back from the bottom of backpacks and lockers--I might try something quarterly like that this year. For the most part I don’t think students are wanting to steal books (and if they are, maybe it’s a book they REALLY love and that’s not the worst thing!) but they might forget to look under their beds and in the very depths of their backpacks. Overall I prefer to keep the system informal--I want to create as few barriers as possible to students’ access to books. Particularly for reluctant readers, I want it to be as simple as possible for them to slide into a “reader” identity from a “not a reader (yet)” identity. Books do cost money, so I may look into a scanning system this year. I’ve read about a few recently that seem simple to use, and might even help students know if a particular book is in our library, which might be more useful to me than a check-out feature. It might help me better analyze what aspects of the library need a boost in a way that is more reliable than my (tired teacher) memory.
Last year I was very lucky and had a group of four students who requested to be the classroom librarians. They came up with their own genre-sort system with color-coded labels. They met once a week to sort the books, shelve returned books, and argue over which books should go in which category. It was delightful! I am thinking about how to recreate this in future classrooms--it’s a great space for collaboration, appreciating book design, and discussing books informally.
Here are some useful links related to classroom libraries. I haven't tried all the tools and resources but have been collecting a list of other teacher's recommendations.
CLASSROOM LIBRARY RATIONALE:
LIBRARY ORGANIZATION TOOLS: