This is provocative.
Consequently, I have sought studies that would support the original contention that we could facilitate student learning by placing kids in the right levels of text. Of course, guided reading and leveled books are so widely used it would make sense that there would be lots of evidence as to their efficacy.
Except that there is not.
....The problem with guided reading and similar schemes is that they are focused on helping kids to learn with minimal amounts of teaching (something Pinnell and Fountas have stated explicitly in at least some editions of their textbooks). But that switches the criterion. Instead of trying to get kids to optimum levels, that is the levels that would allow them to learn most, they have striven to get kids to levels where they will likely learn best with minimal teacher support.
It's by Timothy Shanahan. He teaches at the University of Illinois at Chicago, and used to be literacy director for Chicago Public Schools.
I read some more of his stuff. He writes:
I've written often in this space about the need to ramp up text difficulty. But in doing that we need to be sure not to overdo it.
In contradiction to past theories of how someone learns to read effectively, I have put forth the idea that students probably benefit more from working with a range of difficulty levels (much as athletes train at varying intensities and distances).
Rigor is the new black.
I.e., he believes students should frequently be asked to read above their "reading level," while acknowledging the challenges therein.