[Monitor]

What I don't get is, why? It's a lot simpler, isn't it, to just explain why you have to carry a one into the tens column.

Maybe not if you're trying to do it in your head. So, you memorized all the way up to 13 x 13. What's 14 x 15?

Here's how I would do it.

14 x 15 = (10 x 15) + (4 x 15) = 150 + 60 = 210.

Or, taking the lesson to it's absurd extreme, maybe it's 150 + 50 + 10 = 200 + 10 = 210.

You want to multiply five times 4, is 20, so zero, carry the 2.

Five times 1 is 5, plus the 2, is 7. That makes 70.

Ten times 14 is is 140, plus 70 is 210.

Same answer, but I'd much rather do it using 10s, 20s, 100s, etc, which is obviously the point of this exercise. Being able to do math in your head, beyond what you've managed to memorize, is a damned good skill to teach kids.

[RansomOttawa]

Maybe not if you're trying to do it in your head. So, you memorized all the way up to 13 x 13. What's 14 x 15?

14 x 15 = 7 x 30 = 210.

One step, extrapolating from what I learned by rote when I was 8.