Lesson objective: Subtract two three-digit numbers involving regrouping 1 ten to make 10 ones, or 1 hundred to make 10 tens.

Students bring prior knowledge of adding and subtracting three-digit numbers from 2.NBT.B.9. This prior knowledge is extended to problems that require regrouping as students regroup 1 hundred to make 10 tens, or 1 ten make 10 ones. A conceptual challenge students may encounter is understanding equivalent forms of three-digit numbers.

The concept is developed through work with base ten blocks, which supports the idea that numbers can be regrouped in different ways to add and subtract.

This work helps students deepen their understanding of operations because students are provided with multiple ways to represent and model missing addend problem situations.

Students engage in Mathematical Practice 8 (Look for and express regularity in repeated reasoning) as they solve three-digit subtraction problems using previously learned strategies. Students will also apply regrouping strategies from two-digit subtraction to three-digit subtraction. Base ten blocks, number lines, and strategies related to place value will support students' understanding in this lesson.

**Key vocabulary:**

- base ten blocks
- decompose
- digit
- equivalent
- hundreds
- number line
- ones
- place value
- regroup
- tens