Should librarians police students’ reading-level selections?

Elementary school administrators, educators and librarians (and any other informed stakeholders), what do you think of students being expected to always read at their designated level, with the librarian required to prevent them selecting books that are “below” their level?

I prefer the position advocated by Regina Powers, writing for American Libraries magazine: “Encourage readers to first find books on the shelf that they are interested in reading and only then to look them up to find out whether a quiz exists or point value is issued.”

I agree with Powers that a computer-generated readability formula and the number of points to be awarded for passing a comprehension quiz have nothing to do with a book’s complexity of themes or its potential for enjoyment. As Powers points out, “Authors don’t write books to a targeted reading level. Authors write stories or fact-filled books that they hope readers will enjoy.”