I think a lot of the issue with common core is the way its taught. I saw some question like how to get 10 from 8+5. They were trying to teach the kids that adding is easier if you know that 8+2=10 and 5-2=3 that you can get to 13. I probably just did as bad a job explaining it as the question did.
Something like the above concept I got intuitively at some point but other concepts I see from common core blow my mind.
Yeah, those "samples" that get shared around the Internet like they're somehow standard Common Core are really misleading. The kids in my daughter's class did hands on math. They'd draw it, break numbers apart, do whatever made sense to them to see how the process worked. Because of that, the algorithm became just a natural discovery. Common core doesn't teach "this is how you do it in a weird way". It asks "how can you figure out how to do it", and then the algorithms make sense. Like I said, these kids have never seen a times table or math facts, but they do math better than a lot of adults I know and actually understand how it works.
For my daughter, multiplication is just chunking (if she saw 12 x 13, her brain would just split 12 x 10 and 12 x 3 and then add them up intuitively). Because she learned it on her own, it's a rapid process. Algorithms would have taught her to multiply digits and carry and so many steps she wouldn't need. When I first showed her how we multiply using the algorithm, it made sense to her immediately because she knew why it worked.
It's the same with the reading. They're learning how to analyze instead of summarize. That's the part that has frustrated English teachers at the high school level, because they do long, deep reading now, looking at quantifiable arguments instead of reading a book and just talking about it in whatever way you feel. There's no BS.
