Note: This question has been cross-posted to MathOverflow: see here.
I am witnessing a new curriculum change in my country (Iran). It includes the change of all the mathematics textbooks at all grades. The peoples involved has sent me the textbook for seven graders (13 years old students) to have my ideas about the book. The book starts with Polya's famous four steps of problem solving. Then it continues with "teaching" a bunch of problem solving strategies. That is the first chapter of the book. As a mathematics educator I am against separating "problem solving" from "solving problems" (at least, for such young students). However, obviously as a MSE question I am not up to discussion. Instead, I am looking for the facts.
I am aware that years ago it was a common approach in the USA to have a separate chapter like the one I described in the mathematics textbooks. Are such textbooks still in use? If yes, at what grade (or at what age), and in which country?
PS. Probably you are not living in a country with a centralized system (in which all students at a certain grade use the same book). If this is the case, it would be great if you just mention the book you are aware of, or you have experienced.
This may not completely answer your question (an important question as well). I am in Australia, and relatively recently, we have been implementing a national curriculum, I am also a Maths (and Physics) teacher.
In researching this kind of problem, I came across this Australian conference proceeding Mathematics Curriculum Development and the Role of Problem Solving. This article doesn't just look at Australia, it draws on examples from many places around the world.
An important point from the article is:
I have seen some textbooks from here and when I worked for the IB (in Japan), that have a separate problem solving skills chapter, but also include skills development within each topic chapter, an example is this year 10 textbook (Chapter 11 is a problem solving chapter).