I think that "problem solving" shows up in one way or another in most textbooks in Germany, mainly in grades 8 or 9 (age 14-15). Unfortunately, the only problems to be solved with these strategies are standard routine problems. These books do not contain any challenging geometry or algebra problems at all, which is no surprise since the latest reforms in Germany have almost completely removed geometry and algebra from the curriculum. The whole idea seems to be that you can learn problem solving by not solving problems. Needless to say: this does not work.

In general, teaching problem solving is a very good idea if the teacher in question knows how to solve problems.