At my old school, all the books had "pockets" at the back. I created my own "date due slips" that would fit in these book pockets. My older student volunteers loved to have the job of stamping new due date slips each day. They would cross out the old due date and stamp the new one for all the classes for that day.
I'm at a new school whose books do not have these pockets, and I also could use a suggestion for a new system. Right now I have a book checkout calendar on my door and I also put an announcement about the next book check out dates in the principal's weekly bulletin for teachers to remind their students.
Thanks for putting this question out there!
Best regards,
Aimee