Lesson objective: Understand that you can find ten more or ten less than a value without having to count by ones.

Students bring prior knowledge of place value from 1. NBT.B.2. This prior knowledge is extended to mentally adding/subtracting a group of ten as students are asked to find ten more or ten less than a given value. A conceptual challenge students may encounter is understanding how to change the digit in the tens place to represent adding or subtracting 10.

The concept is developed through work with base ten blocks, which helps students visualize how the value of tens changes while the ones digit stays the same.

This work helps students deepen their understanding of operations because the digit in the tens place increases or decreases by one , depending on whether students add or subtract 10.

Students engage in Mathematical Practice 7 (Look For and Make Use of Structure) as they notice the pattern of the digit in the tens place changing when they are adding/subtracting 10.

**Key vocabulary:**

- adding
- digit
- take away
- tens
- tens place
- ones
- ones place
- place value
- subtracting
- value

**Special materials needed:**

- base ten blocks