Lesson objective: Extend understanding that we can compose and decompose numbers from 11 to 19 into ten ones and some further ones.

Students bring prior knowledge that the numbers 11-19 are composed of ten ones and one, two, three, four, five, six, seven, eight, or nine ones from K.NBT.1. This prior knowledge is extended to understanding that the numbers 11-19 are the sum of 10 ones and 1, 2, 3, 4, 5, 6, 7, 8, or 9 ones as students begin to be exposed tp equations that involve 10 plus a number. A conceptual challenge students may encounter is understanding the addition sign.

The concept is developed through work with ten frame, which allows students to visualize ten as the first addend in an equation where the sum is 11-19.

This work helps students deepen their understanding of equivalence because they will discover that the numbers 11-19 are equal to 10 plus a number.

Students engage in Mathematical Practice 4 Model with mathematics as they start with a full ten frame and spin the spinner to find their second addend students will begin to understand that the numbers 11-19 are the sum of ten and 1, 2, 3, 4, 5, 6, 7, 8, or 9. Students should represent their work through pictures, numbers, words, and possibly equations.

**Key vocabulary:**

- add
- addend
- compose
- decompose
- sum
- "teen" number

**Special materials needed:**

- counters
- recording sheet
- spinner
- ten frame