## Three-Digit Addition and Subtraction With Regrouping

Developing the Concept

Review the concepts taught in Introducing the Concept. Explain to children that in this lesson they will be learning to add and subtract three-digit numbers without using models.

**Materials:** place-value blocks, half-full jar or cup of approximately 100 paper clips (or any small object), paper, pencils

**Preparation:** Place the paper clips in the jar or cup. Make sure the jar or cup is about half full.

**Prerequisite Skills and Concepts:** Children should be familiar with basic addition and subtraction facts and with place-value concepts. Children should be able to add and subtract one- and two-digit numbers, with and without regrouping.

Group children in pairs. Give each pair hundreds, tens, and ones base-ten blocks, paper, and pencils. Write the number 151 on the board in large print. Leave enough space between each digit to make it clear where the place-value columns are.

**Wrap-Up and Assessment Hints**

Provide children with many opportunities to practice adding and subtracting three-digit numbers with and without regrouping. Continually reinforce the importance of lining up numbers so that each numeral is in the correct place-value column. Include exercises that require children to use estimation. Observe children as they work through exercises and offer assistance as needed. Keep in mind that some children may prefer to have base-ten blocks available as they work through exercises. Finally, remind children to check subtraction using addition to be sure their work is correct.