Lesson 20

The purpose of this lesson is for students to estimate whether a group has more or fewer than 10 objects or images.

In previous lessons and units, students represented 10 in many different ways and used these representations to compose and decompose 10. In this lesson, students use their understanding of 10 to estimate how many images there are. Students also assess the reasonableness of given estimates. The focus on understanding the magnitude of 10 prepares students for work with place value in the base-ten system in grade 1.

If students need additional support with the concepts in this lesson, refer back to Unit 6, Section B in the curriculum materials.

• Gather materials from:
  • Shake and Spill
  • Number Race
  • Grab and Count
  • What's Behind My Back?
  • Pattern Blocks

In grade 1, students learn that a group of 10 ones makes a new unit called a ten. How has this work prepared students to understand 10 ones as 1 new unit?