How Can You Teach Subtraction Regrouping with Understanding?

Our third and fourth grades have been making the uphill trek to teach subtraction regrouping.  We have taught kids to first use expanded form/decomposing numbers so that understanding may accompany all of the crossing out/regrouping that occurs.  I started out calling it expanded form, but then I realized that having the plus signs in the expanded form would cause confusion when kids are actuallysubtracting.  More accurate language would be “decomposing the numbers”.  Anyhow, we used the method of decomposing numbers after students had lots of experience with base ten block subtracting.  Some students are still using the base ten blocks to subtract because their understanding of the number decomposition isn’t there yet.

Subtraction Regrouping with Number Decomposition

Subtraction regrouping takes at least two weeks to perfect in my experience.  After the students have had ample experience decomposing numbers with subtraction regrouping, then we move to the traditional algorithm using the same language we did when the numbers were decomposed–that is we make sure that we call the tens we are marking out tens etc.  For example, if we cross out a seven in the tens place to write a six above it, we call it six tens NOT six.  To help students’ understanding, it is important that the teacher language is precise and that the students are held accountable to use precise language as well.

One last side note:  This week when I was working with an intervention group, I noticed that some students looked confused when I said the word regroup, so I changed my language.  I called regrouping exchanging.  They still looked confused so I changed my vocabulary again to the word trade.  Students seemed to understand that better.  I think that is something that kids are familiar with.  They are always talking about trading a baseball card, something on their lunch plate, a piece of candy etc.

Happy teaching!