The "assumed" skill: Speaking!
We can all "speak" -- right? It is, after all, assumed that a normally-healthy human being develops speaking skills, although some learn to do it better than others. It is speaking that sets us apart from other animal, so they say. For the most part, we aren't taught speaking as a distinct skill as we develop our first language skills, unlike reading, writing, and (perhaps) listening.

Scott Thornbury's approach in How to teach speaking will surprise you.

Probably even the least trained teachers recognize that speaking is more than simply producing orally the planned language we produce in writing. But other than subskills like pronunciation and perhaps the distinct grammar of casual speech, is it really worth this much attention? Well...
Surprise, Surprise
Sometimes experienced teachers developed established routines or expectations that can lead to rude awakenings in the classroom with a new class of students. So too, we can be surprised when a book tackles a subject in ways other than expected. That can be good, after the initial discomfort.
Scott Thornbury's approach in How to teach speaking will surprise you. Ultimately, in a good way. Take the time to warm up to a new way of doing!
Recognizing what we are talking about
When we think about it, a "speaking" class and a "conversation" class aren't really the same thing, although we often casually interchange these terms. I was somewhat uncomfortable through much of my initial spin through How to teach speaking because I was expecting a "how to teach conversation" book. And because Thornbury's presentation is rather different than we have experienced in Jeremy Harmer's series opener How to teach English and other major series in basic teacher training, like David Nunan's Practical English language teaching and Kathy Bailey's Practical English language teaching: Speaking. Such surprises can be irritating, at least at first. But remember, it is the irritation in the oyster that generates the pearl.
Attacking the issues in a different way
The opening chapters deal with speaking generalities, using the first language context, in the same way that Second Language Acquisition is often taught by first examining what happens in the L1. The problem here is that the short introduction to the book doesn't really make clear that we are attacking the problem in this way. A more expansive introductory chapter, or some indication on the back cover, describing this framework, would clarify matters tremendously.
Also different, but in a good way, is how Thornbury tackles terminology. Assuming that teachers and teachers-to-be are intelligent human beings who enjoy intellectual stimulation, new terminology is presented in context, with supportive descriptions but without the simplistic or over-technical definitions that burden so many other books. While a glossary is often helpful, the index for this book will guide most readers to the pertinent description should they lose track later on in their readings. Thornbury provides more technical vocabulary than many other texts, which will serve a teacher well as they enter discussions on this topic with peers or continue their readings elsewhere. Avoiding such language is a short-cut to future embarrassment.
The practical focus of the book is most clearly evidenced by the fact that the text is not burdened with references to obscure scholarly works. A concise set of further readings are organized by chapter at the back of the book. Those who want to explore more will go there.
Once we have worked our way into Chapter three, where L1 and L2 speaking is distinguished, we have grown accustomed to Thornbury's design, and it all begins to make a lot of sense.
Awareness-raising, Appropriation, and Autonomy
Chapters four through six are the type of things most of us were expecting from such a book. Activities. The strength of this book is that they aren't a mere hodge-podge of ideas, but are founded on the theory presented earlier. Here the first "practical classroom application" appears, with it's clever little margin icon -- a chalkboard! Really nice stuff here. It's not just photocopiable exercises, which you can find elsewhere. This is structure that allows teachers to understand the “why” and develop their own. It draws upon the strengths of the CELTA design of instructing novice teachers: demonstrating practical classroom devices with imagery and example.
Planning and Assessing
The final unit could be the first in many contexts. Do we need to teach speaking in our educational context? If we teach it, then, how do we assess? Here assessment refers to both the learner, which of course does make sense at the end of the book, but also, assessing institutional and learner needs. Do we need to teach speaking???
There is an interesting little mention of genre-based teaching as an alternative to task-based teaching, and here, as throughout, Thornbury's concern for the grammar and vocabulary aspects of speaking are visible. Clearly this is not your prototypical turn-of-the-century "task is all" approach to teaching speaking.
Self-Study Tasks
The Task Files at the back of the book provide useful post-reading exercises, with references to the pages where the discussion of the underlying knowledge is presented. Better still, there is a KEY! (So often missing in other books where activities are presented.) Placing this at the end of the book rather than after each chapter is but one more of this book’s alternative approaches.
And so...
There is always more than one way to tell a story. Sometimes it takes a different presentation before people really get it. Scott Thornbury's How to teach speaking is an important contribution to the teachers' library because it offers a different path. And as Robert Frost reminds us, "that has made all the difference."