Lesson objective: Add by composing and decomposing 10.

This lesson helps to build procedural skill with composing and decomposing 10. An arithmetic rack is used here because it highlights the total 10, both visually and kinesthetically. This work develops students' understanding that addition can be thought of as putting together and counting on.

Students engage in Mathematical Practice 1 (Make sense of problems and persevere in solving them) as they use an arithmetic rack to solve problems, thinking of addition as putting together and counting on.

**Key vocabulary:**

- arithmetic rack
- number partners

**Special materials needed:**