Lesson objective: Compose and decompose numbers from 11 to 19 into ten ones and some further ones.

This lesson helps to build fluency with composing numbers 11-19. Cups filled with counters and ten frames are used because they support students' understanding of ten ones and some more ones that create teen numbers. This work develops students' understanding that the numbers 11-19 are composed of ten ones and one, two, three, four, five, six, seven eight, or nine ones.

Students engage in Mathematical Practice 7- Look for and make use of structure as they explore the base ten system as it relates to the numbers 11-20. Students see how each number is created from ten ones and some more ones.

**Key vocabulary:**

- compose
- decompose
- "teen" numbers

**Special materials needed:**

- counters
- cups
- recording sheet
- ten frame