E and His "Just Right" Book

I met with E today and his "just right book" was way to easy. We read over 1000 words. He only made three errors. It is important to have student autonmy in the classroom but students still need to be challenged. When do is it ok for E to have a "just right book" and one that he is more comfortable with? The challenge is to find this balance so that students are still challenged yet have choice in the classroom. Will I be able to know my students well enough that all have a just right book but at the same to have books that they can read and just enjoy and be comfortable.

I know for myself I need to pick up a $6.99 romance novel that can be read in three hours which I don't have to use any brain power to read, after reading academic texts and informative articles throughout the quarter. Should students in the classroom be given this "time off" as well?