Learning Objective: At the end of this lesson, students will be able to add two-digit numbers within 20.

Materials: Individual whiteboards and markers, two-digit number cards

Procedure: 1. Begin the lesson by asking students what they already know about adding numbers. Discuss any potential answers they give and write some examples on the board. 2. Ask students if they have ever added two-digit numbers before. Discuss the steps they took and be sure to point out why it is important to start with the larger number. 3. Show students the two-digit number cards and ask them to come up with all the combinations they can make by adding two cards together. Write all the examples on the board. 4. Explain to students the strategy of “counting all” when adding two-digit numbers to get them familiar with the concept. Show them how to count all on the individual examples they came up with, and explain why it is important to start with the larger number again. 5. Ask students to practice adding two two-digit numbers on their whiteboards. Give them one number and have them add it to each number on the card until they have all the combinations. 6. Once students have practiced, give them small assessment questions to check for understanding. 7. Review the objectives from the lesson and discuss formative assessment.

Closure: Discuss any questions or difficulties students may have had with the material. Reinforce the concept of counting all when adding two-digit numbers and explain why it is important to always start with the larger number. Finally, review the learning objectives to ensure students can appropriately apply the strategy.