# Lesson 10

Center Day 2 (optional)

### Lesson Purpose

The purpose of this lesson is for students to practice adding and subtracting within 100 using methods based on place value understanding, the properties of operations, and the relationship between addition and subtraction.

### Lesson Narrative

This lesson is optional because it is an opportunity for extra practice with addition and subtraction within 100 that not all classes may need. In Activity 1, students learn stage 5 of the Target Numbers center which was introduced in a previous lesson. In this new stage, called Subtract Two-digit Numbers, students roll number cubes to create two-digit numbers from a starting number to get as close to 0 as possible. In Activity 2, students chose to continue working on Subtract Two-digit Numbers, or choose between two previously introduced centers focused on addition and subtraction within 20.

As needed, revisit and reinforce the structures and norms for centers that were established in previous lessons.

### Learning Goals

Teacher Facing

• Add and subtract within 100.

### Student Facing

•  Let’s play games to practice adding and subtracting.

### Required Materials

Materials to Gather

Materials to Copy

• Target Numbers Stage 5 Recording Sheet

### Required Preparation

Activity 1:

• Each group of 2 students will need 3 number cubes.

• Each group of 2 students will need base-ten blocks to represent at least 20 tens and 18 ones.

Activity 2:

Gather materials from:

• Target Numbers, Stages 4 and 5

• Capture Squares, Stage 3 and 4

• Five in a Row, Stage 6

### Lesson Timeline

 Warm-up 10 min Activity 1 20 min Activity 2 20 min Lesson Synthesis 10 min

### Teacher Reflection Questions

As students worked together today, where did you see evidence of the mathematical community established over the course of the school year?