Thank you for saying this. I am/was a high school math teacher and this was always the biggest problem when we got students in. The teachers at lower levels just don't understand it well enough to teach it. And, sadly, the same can even be said to be true for some of my coworkers. Our calculus teacher hasn't retired yet because there's nobody she trusts enough in the math department to understand pre-cal/calculus well enough to teach it (I'm on a leave of absence and have switched to the science department, though I've been asked by her and admin to teach those if I return).
To me, common core math makes perfect sense. It's how I do math in my head. But it's also because I feel like I understand math. If I'm subtracting 26 from something, I'm going to subtract 30 and add back 4. It's just quicker and simpler. That's what I've seen parents struggling with, and even teachers struggle with it too! Because they don't get how numbers work. It's really frustrating and harms the kids. I wish I could overhaul how elementary school teachers are trained as in my state they're not even required to do well in math, or take any upper level math courses, before teaching math.