Lesson objective: Understand that numbers can be taken apart.

Students bring prior knowledge of addition from** **** **K.OA.A.1 and K.OA.A.2. This prior knowledge is extended to contrast the new concept of subtraction as students learn that number can both be composed and alternatively decomposed. A conceptual challenge students may encounter is thinking that when a number is decomposed into groups, this action increases the total in the set.

The concept is developed through work with objects and fingers, which provide students with a consistent set of five leading to 10. Students learn to subitize small groups in larger groups with a tool they literally carry with them. Connections to written representations such as a number bond or five frame allow students to begin to organize their discoveries.

This work helps students deepen their understanding of number because a set can be taken apart into more than one group or separated individually. The total in a set is the same regardless of how it is arranged or taken apart.

Students engage in Mathematical Practice 4 (Model with mathematics) as they use their tools to solve a real-life problem and record their thinking using numbers and drawings.

**Key vocabulary:**

- count
- five frame
- number bond
- subtraction
- take apart
- total

**Special materials needed:**

- counters in two colors
- five frame
- number bond
- record sheet (or other tool to record thinking)