[A_perfect_lady]

I suspect they are trying to teach kids ways to subtract if they don't have paper and pencil handy and have to do it in their heads. It can be difficult to hold the image in your mind that you would have in front of you if you had paper.

Personally, if I were trying to solve 427-316 in my head, I too would first take off the 300, and say to myself "Okay, now it's 127-16." Then I'd take away the 6 and think "Okay, now it's 121-10," and from there I'd be okay. I think that's what they're trying to teach here.

[KarlInOhio]

One problem I have with many of the common core fights is that we don't see the entire text book, but only a few pages to get outraged about. Are the methods used for a few days or weeks to try to get concepts across which will then be used to teach standard methods, or are they dead ends which are muddleheadedly taught until calculators are thrown to the kids? Have there been real side by side studies on teaching different groups of students different methods to see which method ends up with the best education? Or do you just have a bunch of educational profiteers coming up with "new" methods to sell text books because otherwise schools might just keep their old text books for free, thus leaving education professors without the extra pay from writing new texts.

Then, on top of that, is the constant suspicion that the government wants to bring up a generation of compliant drones rather than educated citizens and common core is the path to do that.

[HiTech RedNeck]

Even there, describing how to translate the problem doesn’t need a number line. The various stages (X - Y) = ((X - 10) - (Y - 10)) could be put down as such.