Three-Digit Addition with Base-Ten Models

Explicit Instruction/Teacher modeling

• Begin by displaying the ones unit block from your base-ten block set on your document camera. Ask students to volunteer what this represents.
• Do the same for the tens and hundreds pieces.
• Review the meaning of digit and explain we will be working with three-digit numbers today.
• Using the base-ten blocks, make a three-digit number (e.g. 246) on the document camera. Ask students to turn and tell a partner the number.
• Ask students, "How can we represent this number if we do not have blocks? Is there a way to draw them?"
• Show students that each hundreds block can be represented with a large square, each tens block can be drawn as a thin rectangle, and each one block can be drawn as a small square.
• Demonstrate by drawing the number 246 in three columns (labeled H, T, O), keeping the hundreds on the left, the tens in the middle, and the ones on the right.
• Introduce a second three-digit number, such as 152.
• Draw 152 directly underneath 246 so the hundreds, tens, and ones are aligned.
• Have partners turn and talk about how to add these two numbers using our drawings.
• Demonstrate adding the numbers starting with the ones place and moving left. If regrouping is needed, you can cross out and add to the column on the left.

Guided Practice

• Have student helpers assist in passing out whiteboards, markers, and dry erase markers.
• Instruct students to draw the three columns labeled H, T, and O.
• Give students two or three problems to solve using base-ten drawings. Make sure at least one problem includes regrouping.
• After giving students time to solve each one, have students hold up their whiteboards so you can assess understanding.
• Assist struggling students.
• Have student helpers collect whiteboards, markers, and erasers.

Independent working time

• Distribute the Triple-Digit Addition worksheet and scrap paper.
• Instruct students to write their names on both pages.
• Explain that the worksheet is where they will write their answers and the scrap paper is where they will show their work using base-ten models for each problem. Demonstrate on your own copy of scrap paper how to label their work with the corresponding number from the worksheet, so you can quickly check their work.
• Allow students to work independently on the problems as you circulate the room answering questions.