Lesson objective: Use number line diagrams to solve addition and subtraction problems, which describe "adding to" or "taking from" situations with a missing result, start, or change.

This lesson helps to build fluency with whole number addition and subtraction. Number line diagrams are used here because they highlight part-whole relationships and support the strategy of "counting on" to find a missing addend or "counting back" to subtract. This work develops students' understanding that we can use a number line to solve many types of addition and subtraction problems.

Students engage in Mathematical Practice 6 (Attend to precision) as they label number line diagrams precisely. They also engage in Mathematical Practice 7 (Look for and make use of structure) as they look for number patterns and relationships on the number lines to develop computational strategies.

**Key vocabulary:**

- addend
- count back
- count on
- difference
- number line diagram
- terms for main types of addition and subtraction situations: put together/take apart; compare (*Students do not have to master these terms; however, they may facilitate conversation.)

**Special materials needed:**

- blank number line diagrams (optional)