Gives them more time to work with lower readers. All books are leveled by the same formula. Teachers love the proof of having the AR record to present to parents at conference time. Teachers and students know their zone of proximal development and books can be selected accordingly. Kids finish more books and read more.
Disadvantages Turns kids off of reading, especially if grades are given.
Problems arise when teachers become fixated on points and reading levels. Discourages free reading, love of literature, and reading non-fiction. The faculty sometimes dictates the selection policy for the Media Center. They want nothing but AR books. It's difficult to get kids to read books that are not on the AR list.