Lesson 9

Add Three-digit Numbers

Lesson Purpose

The purpose of this lesson is for students to add 2 three-digit numbers.

Lesson Narrative

In previous lessons, students added a two-digit number and a three-digit number. They shared and compared methods and representations that showed adding by place and composing units.

In this lesson, students practice adding within 1,000. They add two three-digit numbers using methods based on place value and the properties of operations. Students also compare diagrams and drawings to written methods that use equations and expressions. They analyze work to identify why a method worked and identify any errors if the method did not work (MP3).

  • Engagement

Learning Goals

Teacher Facing

  • Add 2 three-digit numbers using place value strategies that include composing 2 units.

Student Facing

  • Let’s practice adding within 1,000.

Required Materials

Materials to Gather

Required Preparation

CCSS Standards


Lesson Timeline

Warm-up 10 min
Activity 1 20 min
Activity 2 15 min
Lesson Synthesis 10 min
Cool-down 5 min

Teacher Reflection Questions

Reflect on who participated in math class today. What assumptions are you making about those who did not participate? How can you leverage each of your students’ ideas to support them in being seen and heard in tomorrow’s math class?

Suggested Centers

  • Five in a Row: Addition and Subtraction (1–2), Stage 7: Add within 1,000 without Composing (Addressing)
  • Number Puzzles: Addition and Subtraction (1–4), Stage 4: Within 100 with Composing (Supporting)

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