We have a very long scheme at DS school, he was level 5c before they put him onto free reading. However, the teacher had moved others on earlier, as they were reading lots of school books, whereas DS was reading more of his own choice at home.
Free reading includes some schooly books like condensed Shakespeares, (yuk) but also real books such as Artemis Fowl, Wolf Brother etc.
When I read at school with Y6 children, if they have already started the book, I ask what's it about, are you enjoying it etc., before we read, and this week it was painfully obvious that some of the "free readers", really did not understand the stories.