Lesson objective: Subtract numbers within 20 using counting up and counting back on a number path.

This lesson helps to build procedural skill with whole number subtraction. A number path is used here because it is the best tool for demonstrating counting up and counting back with subtraction. This work develops students' understanding that strategies such as counting on and counting back can be used to subtract numbers.

Students engage in Mathematical Practice 2 (Reason abstractly and quantitatively) as they use multiple representations, such as a number path and equations and contexts in story problems, to subtract numbers within 20.

**Key vocabulary:**

- count back
- count on
- counters
- difference
- greater
- less
- minus
- more
- number path
- strategy/strategies
- subtract

**Special materials needed:**

- counters, if needed for in-class practice