Lesson objective: Understand that the numbers 11-19 are composed of ten ones and one, two, three, four, five, six, seven, eight, or nine ones.

Students bring prior knowledge that every number 1 to 9 has a partner such that the two numbers can be composed to make 10 from Grade K, Unit 12, K.OA.A.4. This prior knowledge is extended to include composing the numbers 11-19 as students group the ten ones and see the extra ones that form a teen number. A conceptual challenge students may encounter is thinking that the numbers 11-19 are each separate units and not a continuation of the counting base-ten pattern.

The concept is developed through work with a ten frame and counters, which shows that the numbers 11-19 contain ten ones and some extra ones.

This work helps students deepen their understanding of numbers because it will introduce the base ten system and how 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 4 -model with mathematics -as they demonstrate how to count efficiently with an organized system. Students will discover how making a group of ten is a more efficient way to count the numbers 11-19 by providing students with a place to group the ten and then have some extras left over. Give the students a ten frame to put the ten in and see the extra. This should lead to students discovering there are 10 ones and some more ones.

**Key vocabulary:**

- compose
- decompose
- "teen" numbers

**Special materials needed:**

- cup for each student or pair of students with 11-19 counters/jellybeans in it
- ten frame