In math, mistakes are welcome! This lesson helps your students identify and fix errors made while comparing three- to four-digit numbers. Teach the lesson on its own or as support to the lesson Let's Compare Whole Numbers!

Many students cringe when they see a subtraction problem with multiple zeros. The “Subtract One” strategy in this lesson involves reducing the top number by one to turn the 0 digits into 9’s and then adding the one back in at the end.