Lesson objective: Fluently add and subtract within 20 using mental strategies.

This lesson helps to build fluency with adding/subtracting within 20 using mental strategies. The game "Closest to 20" is used here because it requires students to think about number combinations that will be close to 20. This work develops students' understanding that knowing some addition and subtraction facts from memory helps us solve new addition and subtraction problems.

Students engage in Mathematical Practice 1 (Make sense of problems and persevere in solving them) as they draw from their own toolkit for solving problems and utilize strategies that have proven to be efficient for them.

**Key vocabulary:**

- addend
- difference
- equation
- mental calculations
- sum

**Special materials needed:**

- Closest to 20 direction sheet (1 per group)
- Numeral cards (2 sets of 1-9)
- Recording sheet (1 per student)