Lesson objective: Identify when composing a new ten is necessary when adding two numbers.

Students bring prior knowledge of using place value from 1.NBT.B.2. This prior knowledge is extended to using place value to help them add as students solve equations with two-digit numbers and often need to compose a new ten. A conceptual challenge students may encounter is understanding that ten ones can be grouped to make one ten.

The concept is developed through work with base ten blocks and written notation, which helps students clearly see the tens and ones and opportunities to compose a new ten.

This work helps students deepen their understanding of equivalence because 10 ones and 1 ten have the same value.

Students engage in Mathematical Practice 7 (Look for and make use of structure) as they recognize that ten ones is the same as one group of ten. This will help them be able to compose and decompose numbers to add more efficiently.

**Key vocabulary:**

- base ten blocks
- compose
- decompose
- digit
- equation
- model
- ones
- tens

**Special materials needed:**