Here I’ll put resources related to Problem Solving and the Common Core State Standards for Math.
PS and CCSSM
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 are students will be better problem solvers – and therefore better off mathematically and better prepared for the STEM …
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.