Lesson objective: Understand that for any number one to nine, there is one number we can add to it to get 10.

Students bring prior knowledge of seeing addition as adding on to a quantity from earlier work with K.OA.3. This prior knowledge is extended to adding on to make exactly 10 as students count on from a given number to make 10. A conceptual challenge students may encounter is incorrectly believing that there is more than one number partner that can make 10 for each number one to nine. Some students may also struggle to correctly count the number of objects they are using to represent the compositions due to a lack of of one-to-one correspondence.

The concept is developed through work with a 10-frame, which structures the counting and helps students track the total of 10 objects while also tracking how many objects they are counting on.

This work helps students deepen their understanding of number because while students are adding on in order to compose pairs of numbers to make 10, they are developing their understanding of 10 and their ability to anchor other number concepts in 10.

Students engage in Mathematical Practice 7 (Look for and make use of structure) as they notice that there is only one number that is added to each number one to nine that will make 10. The ability to make 10 is also foundational to place value understanding.

**Key vocabulary:**

- compose
- count on
- decompose
- make a 10
- number bond
- 10-frame

**Special materials needed:**

- 10-frames
- two-sided counters (commercial or painted lima beans)