# Lesson 17

### Lesson Purpose

The purpose of this lesson is for students to look for and use patterns to add within 20. Students see that they can decompose one addend in order to make a ten.

### Lesson Narrative

In previous lessons, students recognized the $$10 + n$$ structure of teen numbers and used the structure to find the sum of three numbers. In this lesson, students use the structure of the 10-frame to find the sum of two addends when one addend is 9. Students come to see that when they find the sum of two addends, they can decompose one addend to make 10 with the other addend (associative property). For example, $$9 + 5 = 9 + 1 + 4 = 10 + 4 = 14$$. When students identify and use equivalent expressions, they look for and make use of structure (MP7) and here they repeatedly make a 10 to find the value of expressions (MP8).

Student methods are recorded with equations. It may also be helpful to represent how one addend is decomposed in order to make a ten.

• Engagement
• MLR7

Activity 2: Clare’s Birds

### Learning Goals

Teacher Facing

• Analyze methods for adding within 20 that involve making a ten.
• Look for and use patterns in addition expressions to add within 20.

### Student Facing

• Let’s look for patterns and think about making 10 as we add.

### Required Materials

Materials to Gather

### Required Preparation

Activity 1:

• Each group of 2 needs a set of Number Cards (0-10).

### 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

What was the best question you asked students today? Why would you consider it the best one based on what students said or did?

### Print Formatted Materials

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