Chapin and her co-authors have written a useful guidebook to using talk in math class to advance student understanding. The ideas are great and provide a foundation for starting a discussion based approach to mathematics instruction. However, I found the text repetitive in parts.
Relatively dry writing, but excellent case studies and examples of how to have powerful, on-track discussions in math. I especially appreciated the many, many ideas for troubleshooting unsuccessful math talk.
recommend to teachers of math everywhere, although you'll get bogged down with the never ending examples. it's worth the read. the only way we're going to move forward in mathematics education is by having students talk about their thinking.