Let's Build It! Two-Digit Addition

Explicit Instruction/Teacher modeling

• Read the student objective and define the key words with the students—two-digit numbers (one whole number in both the ones and tens place) and bas- ten blocks (a manipulative used to teach math).
• Use a place value chart (a tool used to teach place value) and base-ten blocks to demonstrate 54 and 3. (Tip: Mention there are 10 of the ones (units) in a rod and show how ten ones adds up to one rod.)
• Write the numbers 54 and 3 on the board, and use five lines to represent five rods and three dots to represent the ones.
• Write 54 + 3 on the board, along with the base ten visual representation.
• Model adding the ones and then the tens on the board to get the total remaining two-digit number (57).
• Solve one more problem that requires the students to carry, or convert, 10 or more ones into a rod (26 + 4 or 39 +8).
• Require students to draw on their whiteboards the equation and base-ten blocks as you solve the problem on the board while asking questions (such as, “Should we keep all 12 ones as dots? Why should we make the 10 ones into a rod? How would we write the visual into equation form?").
• Say, “Now that I’ve shown you how to visually create two-digit numbers with base-ten blocks and add up two-digit numbers, we will practice some more together and in partners.”

Guided Practice

• Speed-practice drawing the numbers on the whiteboard and holding up their answers.
• Do this three times with the numbers 44, 16, and 8.
• Assign students a partner and two problems to solve together (65 + 20 and 33 + 9).
• Review partner answers with the class. With 33 + 9, monitor to make sure they were able to convert the 12 ones into another rod and two ones for a total answer of four rods and two ones.

Independent working time

• Say, “Now you will show me how you can add two-digit numbers with base-ten visual models.”
• Pass out the Count and Add Blocks worksheet and explain the directions.
• Reinforce the use of the base-ten blocks in both written form and the actual blocks for assistance.