Here I’ll put resources related to Problem Solving and the Common Core State Standards for Math.
PS and CCSSM
Does our approach to teaching math fail even the smartest kids?
This article point out the importance of problem solving. This article is not on the Common Core directly. However, I think it is related. If we teach the CCSSM correctly (including the Mathematical Practices) I think our students will be better problem solvers – and therefore better off mathematically and better prepared for the STEM …
The Art of Problem Solving
https://www.artofproblemsolving.com/ This is a great site with a huge database of problems from contests (such as the AMC8, 10, and 10). It is for gifted education but also regular education. Also had Proofs Without Words.