A couple of weeks ago I shared some tips and tricks for 2 Digit Addition with Regrouping. Today I want to break down what has worked best for me when teaching subtraction with regrouping to 2nd graders. Many of my same methods still apply, but I hope you will still find this helpful!
Click HERE to see all of the activities mentioned in this post!
Build Numbers to Subtract
When first starting out (and maybe for quite some time), building numbers is crucial. Regrouping is such an abstract concept that getting concrete with numbers is very helpful. Here’s a little breakdown of how to build a subtraction with regrouping problem:
- Build the total using tens and ones blocks. I built the number 35 with 3 tens and 5 ones.
- Look at the number you must subtract from the total. I need to subtract 18. Go to the ones place. I need to take away 8 ones, but I only have 5 ones. I went over to my tens place and I borrowed a ten. I physically moved that ten into my ones place.
- In order for me to manipulate the number better, I must trade out my ten for 10 ones (after all, a tens block doesn’t belong in the home of my ones!). So, I place 10 ones in the tens place Now I have 15 ones and 2 tens.
- Now that I have 15 ones I can take 8 ones away. I remove those ones. I have 2 tens and I need to take away 1 tens. I remove the ten.
- Now I can see that my answer is 17!
Here’s a video that might help explain it!
Subtraction with Regrouping Chant
Once the students understand HOW to subtract, they must learn how to IDENTIFY when regrouping is necessary. That’s when this subtraction chant comes in handy:
SUBTRACTION WITH REGROUPING: More on the floor? Borrow from next door!
SUBTRACTION WITHOUT REGROUPING: More on top? No need to stop!
ONES PLACE HAS THE SAME NUMBERS: Numbers the same? Zero’s the game!
Repeating this chant often helps to engrain it into the students’ memory. Not every problem is exactly the same, so the chant helps them to remember to pay close attention to that ones place.
Start VERY Slow
Just like with addition, we are going to move VERY slowly through subtraction with regrouping. It’s better to solve a FEW problems correctly than it is to solve MANY problems incorrectly. Let’s redirect, reteach, and remove those bad habits before it’s too late! In 2nd grade, we practice several problems with base ten blocks each day for about a week as a warm-up. We go through every single step. We talk through regrouping. We model, model, model our thinking out loud. Then we get into practicing. I prefer simple activities such as the Solve and Match shown below. It allows students to practice a few problems at a time.
Discuss the Difference between Addition and Subtraction
Since we will be exposed to word problems throughout our unit on regrouping, it is also important to discuss the difference between addition and subtraction. You may have already covered addition and subtraction key words when you were learning facts and strategies at the beginning of the year, BUT it is always good to review!
Check Your Work
Once students have had some time practicing, practicing, and practicing some more, I teach them how to check their subtraction problems by using addition. This is especially helpful when going through problem solving strategies because most require you to either check your work or solve the problem in a new way. One way I like to encourage students to check their work is with this Excellent Elephant! Students show their EXCELLENT work on the elephant’s ears. I can easily check two problems in just seconds to see if they have mastered the concept!
Of course I can’t let you go without sharing a regrouping freebie. I have a Subtraction with Regrouping worksheet for you. This definitely involves the steps I mentioned about taking it SLOW and limiting how many problems students solve.
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