http://misscalculate.blogspot.com/2011/05/purpose-of-textbooks-convince-me.html
I've had this page open in a tab for six months now and I still want to formulate a convincing answer. I'm surprised at how many math teachers take pride in not using a textbook and I wonder about the quality of their alternative materials. Our thinking can't just superficially be about book vs. no book. Instead we have to focus on engaging mathematical tasks as part of a well-designed curriculum, one that shows thoughtful design at the lesson, unit, course, and multi-year levels. Ideally, the text should provide much of that, but I understand that not all texts are created equal.