"Common core" can mean different things to different people. When my kids were in grade school, I found that a few states have put their common core standards in fairly readable form. My impression is that common core is remarkably similar to what my siblings and I learned in K-12 math class. It actually led me to wonder what all of the fuss is about.

The main thing that seems to be lacking in K-12 math today, is proofs. Those were my favorite part of math.

With that said, K-12 math teaching in my generation wasn't all that successful.