Lesson objective: Understand how to use counting on to subtract data from an organized data set.

Students bring prior knowledge of subtraction and counting by ones from K.CC.B.5 and K.OA.A.2. This prior knowledge is extended to using counting on as a strategy to subtract because figuring out how many to count on is the same as figuring out how many were added on. A conceptual challenge students may encounter is believing that counting on can only apply to addition situations.

The concept is developed through work with a real-life data set, which allows students to count on to subtract while modeling the data in a picture or the beginnings of a picture graph and number sentences.

This work helps students deepen their understanding of operations because when we think about how many we counted on, we can use counting to subtract.

Students engage in Mathematical Practice 4 (Model with mathematics) as they organize and represent data in different visual formats. Students will also engage in Mathematical Practice 1 (Make sense of problems and persevere in solving them) as they use the context of data to reason through rich problem situations and use counting on the subtract.

**Key Vocabulary:**

- counting on
- data
- data point
- organize
- picture graph
- represent
- subtract
- take away

**Special Materials:**

- graph paper (optional)