Lesson 2

The purpose of this lesson is for students to fluently add and subtract within 20 to find unknown addends.

In previous lessons, students assessed their fluency with sums and differences within 20. They shared different methods for finding the value of sums and differences mentally.

In this lesson, students find unknown addends within 20 and continue developing fluency with addition and subtraction within 20.

The cool-down should be completed before the lesson synthesis so that students can share their responses during the lesson synthesis.

•    Create a set of cards for each group of 2.

• Each group of 2 needs the digit cards 0–9 from the card set used in the previous activity.

Think about which students haven’t shared their strategies in class lately. Were there missed opportunities to highlight their thinking during recent lessons? How can you take advantage of those opportunities when they arise?