Inside Track: Adding 2-digit Numbers With Regrouping
Adding with regrouping is likely to be the first algorithm children learn after memorizing number facts, the first time they’ve been asked to handle operations that go beyond simple 1-digit questions. In many ways, this operation is the “sister” to 2-digit subtraction that I looked at last week.
Here are some recommendations, also discussed on the video:
Use base ten blocks to illustrate the operation and the regrouping process (see the students’ video below).
As with subtraction, introduce examples that need regrouping from the beginning, rather than allowing students to do easier examples without regrouping first. This is because students can develop “buggy algorithms” if they work out that you can do addition working from left to right, which will cause errors when regrouping is needed.
Addition number facts must be learned before attempting this algorithm. Discourage children from counting on fingers, and definitely don’t allow use of a calculator.