I’m officially trading in my place value blocks for unifix cubes!
Today I was trying to teach a small group of students how to subtract with place value blocks. The problem came when I tried to show how to regroup! As soon as we traded a ten rod for ten ones, eyes glazed over and their minds left me. They couldn’t understand why we’d trade it in and pick up ten ones. I realized that is because it doesn’t really explain the concept, which is that we are breaking the ten into 10 ones, not trading. Instead I tried unifix cubes, which you can actually break apart.
So when I blasted apart a 10 pack of unifix cubes, the light bulbs switched on. The students were so excited to try it themselves, and then, when shown the algorithm next to it, I heard a lot of “OHHHH!!!”
It was the coolest thing. Here is how we did it.
Start with your problem, but only show the top number with the place value blocks.
Decide if you can subtract seven from two. As the numbers stand, you cannot. So…take a ten, and show it on the number below. (The three tens become two tens.)
Break that ten into ten tiny ones.
Those ten ones are placed next to the two that were already there.
Now we have 12 ones! We write it on the problem below to help us understand why we do that.
Now we’re all situated, and we can subtract. When you take seven ones away…
You are left with five ones!
Then, you can take one ten from the two tens.
One ten and five ones remain!
The best part is, teaching this way solidifies MY math and number sense. When I grew up, were were taught how to “borrow and carry” but I had absolutely NO idea why. I learned how to do this as an adult, and it was very difficult to learn. I find that when I understand math more deeply, it is easier to think of different ways to teach these concepts to students who struggle!