My son's in 4th grade, so I've been seeing a lot of Common Core stuff over the last few years.
I used to really hate Common Core.
Then things started to click. Turns out the problem isn't with Common Core in and of itself. The problem is that
no one knows how to teach it correctly.
This video (https://www.youtube.com/watch?v=aLCO6pG6JDY) is a fairly accurate description of the counting-up method of subtraction that's taught as part of Common Core. It seems
ridiculous, doesn't it?
Well, it IS ridiculous, when you do it like THAT.
The problem isn't with the technique, though. Believe it or not, the technique is actually used MORE OFTEN than traditional subtraction with borrowing in the real world.
"I don't believe you, Coda!"
No? Well, check this out:
"39, 40, 50, 60, 70, 80, 90, a buck, two bucks, three bucks, three twenty-five. That's two pennies, six dimes, two dollars, and a quarter; your change is $2.87, have a nice day!"
Why don't they teach it that way in schools? >_< Parents could actually help their kids with their homework!
Every step of that counting-up process is a trivial thing to do in your head. It's all small, round numbers until the very last step -- 2 + 60 + 200 is trivial!