Lesson 3

Sumemos, expliquemos

Lesson Purpose

The purpose of this lesson is for students to add 2 two-digit numbers, without composing a ten, using methods based on place value and to write equations to represent addition methods.

Lesson Narrative

In previous lessons, students used methods based on place value to add within 100, without composing a ten. They analyzed equations that represent methods for finding the sum.

In this lesson, students add two-digit numbers using methods of their choice and write equations to match their thinking. Students interpret and compare different methods for finding the value of the same sums. Students also practice explaining their own methods and listening to the methods of their peers. Students have opportunities to revise how they explain their own and others' methods and consider how representations of their own thinking (for example, drawings or equations) can help them explain or interpret their work (MP3, MP6).

  • Action and Expression
  • MLR7

Learning Goals

Teacher Facing

  • Add 2 two-digit numbers, without composing a ten, using methods based on place value.
  • Write equations to represent addition methods.

Student Facing

  • Sumemos números y escribamos ecuaciones para mostrar nuestro trabajo.

Required Materials

Required Preparation

CCSS Standards


Lesson Timeline

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

Teacher Reflection Questions

Today students were asked to share their thinking in a way that would make sense to their partner. What have you noticed about the language students use? What support can you offer to students who struggle to communicate their ideas orally?

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