Keeping up with Book Boxes- a management tip

This system works so well! Each group has a specific day of the week they are allowed to change books. While everyone else is reading to self, the group of the day is allowed to trade books in the library. The empty squares next to each group is where I write the level they can choose from. It's so simple. It takes a little bit of training, but then book trades run themselves.This leaves me open to conference with other students. Not sure if this is a mind blowing tip, but when I had teachers come observe last year, this is what they raved about so I thought I'd share the idea. :)