Good readers shop for books to read!
Here is a library card to help your students keep track of which level they should be "shopping" in.
Just print out on card stock and write in the level the student is on. I write in pencil so I can erase and change as their levels change. The first circle is for one level below their "just right" level so they can practice fluency with easier books. The middle circle is for their "just right" level, and the third circle is for one level above to give them books that they have to work at and use their strategies.
Clip art is from My Cute Graphics.com