Children are introduced to the concept of regrouping by using tens and ones blocks to show how to regroup 1 ten as 10 ones. This helps to prepare children for regrouping tens when subtracting two-digit numbers. The focus of instruction is on the use of place-value concepts as well as the knowledge of the facts and the strategies for learning the facts. See Addition and Subtraction Facts to 20. When subtracting two-digit numbers, children will discover that they may need to regroup, or exchange, to continue the subtraction process.
Children begin to subtract two-digit numbers using tens and ones blocks.
Once children understand the concept of regrouping, they make the transition from using models to using the subtraction algorithm. To ease the transition, children begin by regrouping to make 10 and 11 in the ones place, which gives children the opportunity to focus on subtracting from zero in the ones place. This is often a difficult concept for children to grasp. Children then continue to develop proficiency subtracting with two-digit numbers by regrouping ten to make 12 to 18 in the ones place. They make the transition from working with the place-value chart to using the algorithm.