dmctavish--
I think you have touched on some important points. "Choice" is such an integral part of what the Sisters talk about for all readers--and I think especially for our struggling readers. They already have the mind-set of not being good enough readers, so we need to change that. Presenting them with a variety of books at their good-fit level and letting them choose gives them ownership--and therefore a reason to practice.
In addition to the Sisters, leaders in reading research (such as Richard Allington) talk about how the most important tool in getting students to become stronger and more independent readers is the amount of time actually spent reading!!