Dr Steven Dykstra kindly provided a couple of links focused on the topic of leveled readers and had this to say:
Dr Steven Dykstra is a member of IFERI's Advisory Group. You can read his statement about his interest in, and commitment to, the reading debate here:Here's the thing about book bands, or leveled readers as we call them here: they are built on a faulty premise.
The theory of leveled readers is that we can order books according to relative difficulty, and that order will be pretty much the same for nearly every child.
Those are two pretty strong claims, each of which needs to be valid for book bands to work as the basis for reading instruction. Simply putting books in order of difficulty is enormously complicated. The systems used simplify that process by measuring length of words and sentences, number of pictures, even the size of the print in some cases. They largely ignore deeper aspects of complexity and writing, leading to absurd results in many cases. These and many other online resource share examples:
http://www.joannejacobs.com/2013/11/stupid-lexiles/
http://leaguewriters.blogspot.com/2012/ ... dents.html
But even if we accept that leveling or banding systems can put books in order of difficulty, should we trust that the order is the same for nearly all children? Given the wide variability between children in terms of their background knowledge, vocabulary, and foundational skills, it is impossible to believe that the order of books arranged according to difficulty will be reasonably the same for nearly all children. What makes a book hard or easy for a given child varies from child to child, especially as we move into more complex literature.
Certainly, a general sense of text complexity is useful to instructors. But it is too variable from child to child to rely on levels or bands as the basis for an instructional system, and the systems of leveling are themselves too flawed to deserve more than minimal trust.
http://www.iferi.org/dr-steven-dykstra/