Lesson 2

The purpose of this lesson is for students to understand and apply counting on and the commutative property in order to find the sum.

In a previous unit, students were introduced to the commutative property in the context of story problems. In this lesson, students consider and use different methods for adding within 10. They relate counting on to addition and consider how the commutative property can help them find the sum more efficiently. Counting on is a method which students use when they are ready, so they may count on for certain sums but count all for others. Students are not explicitly told to count on from the bigger number—this is an understanding that they come to through the work of this and future lessons in which they compare addition methods.

• Each student needs their addition expression cards from a previous lesson to use during the lesson synthesis.

• Each group of 2 needs 10 two-color counters.
• Have one cup available to demonstrate Shake and Spill.

How does understanding the commutative property benefit students as they build fluency with addition within 10?