This classroom library check-out sheet will help you keep track of which students have checked out books. It will also hold students accountable for returning their books in a timely manner and thereby teach them responsibility.
I use this check-out sheet with my middle schoolers in my Readers Workshop classroom. I print them on colored paper (color-coded by class) and stick a bunch of them on a clipboard with a pen attached (because you know otherwise that pen will walk away! ☺) The "class librarian" walks around the classroom about once per month, asking about overdue books - a great way to build leadership, ownership, and community accountability into your reading workshop.