# Lesson 4

Center Day 1 (optional)

## Warm-up: Number Talk: Subtract 2 Digits (10 minutes)

### Narrative

This Number Talk encourages students to think about how to use the addition and subtraction facts they know and their understanding of place value to mentally find values of expressions. The strategies elicited here will be helpful as students use the facts they know to develop fluency with addition and subtraction within 100.

Students may notice that calculating $$6 - 3$$ is repeated in each expression and use this to mentally find the values (MP8). Students must also attend to precision in how they describe how they use known facts or other methods (MP6), especially when they describe subtracting by place. Encourage students to tell more about their strategy if they use unclear language to describe their method and to reflect on how their description could be interpreted differently without more precise language. For example, if students say they knew $$66-30=36$$ because they know $$6-3$$, ask students to explain how that fact helped them subtract.

### Launch

• Display one expression.
• “Give me a signal when you have an answer and can explain how you got it.”
• 1 minute: quiet think time

### Activity

• Record answers and strategy.
• Keep expressions and work displayed.
• Repeat with each expression.

### Student Facing

Find the value of each expression mentally.

• $$6 - 3$$
• $$66 - 3$$
• $$66 - 30$$
• $$66 - 33$$

### Student Response

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### Activity Synthesis

• “How is each expression like $$6 - 3$$? How are the expressions different?” (Each expression has the digits 6 and 3. In each expression you could use what you know about $$6 - 3$$. Some expressions you are finding 6 ones $$-$$ 3 ones. In some expressions you are finding 6 tens $$-$$ 3 tens.)

## Activity 1: Introduce Capture Squares, Add within 20 (20 minutes)

### Narrative

The purpose of this activity is for students to learn stage 3 of the Capture Squares center. Capture Squares was introduced in grade 1. In this stage, students spin to get a number (610) and flip a card (010) and find the value of the sum. The spinner includes a wild space where students can choose their own number. They find the value of the sum on the game board and connect 2 dots that are adjacent to the number. If that line closes the square, they capture it and shade it in their color. The player to shade in 3 squares first is the winner.

### Required Materials

Materials to Gather

Materials to Copy

• Capture Squares Stage 3 Gameboard
• Capture Squares Stage 3 Spinner

### Launch

• Groups of 2
• Give each pair of students a copy of the game board, the spinner and a paper clip, a set of cards, and access to crayons or colored pencils.
• “We are going to play a game.”
• Spin the spinner and draw a card.
• “How could I find the value of the sum of these two numbers?”
• 30 seconds: quiet think time
• 1 minute: partner discussion
• Share responses.
• Use a suggested method or select a volunteer to show how to find the value.
• “Now, I find the square that has the value of my sum. I draw a line connecting two dots on that square.”
• “If the spinner lands on the wild space, you can pick any number to be one of your addends.”
• Repeat 1–2 more times, as needed.
• “If I draw the line that completes the square, I shade in that square with my color. The first player to shade in 3 squares is the winner.”

### Activity

• 12 minutes: partner work time
• Monitor for a variety of student strategies to share in the synthesis.

### Activity Synthesis

• Invite selected students to share their strategies.
• “When the spinner landed on the wild spot, how did you decide what number to pick?”

## Activity 2: Introduce Five in a Row, Add within 100 with Composing (20 minutes)

### Narrative

The purpose of this activity is for students to learn stage 6 of the Five in a Row center. Five in a Row was introduced in grade 1. In this stage, students add within 100 including sums that require composing a ten when adding by place. Partner A chooses two numbers and places a paper clip on each number. They add the numbers and place a counter on the sum. Partner B moves one of the paper clips to a different number, adds the numbers, and places a counter on the sum. Students take turns moving one paper clip, finding the value of the sum, and covering it with a counter. The winner is the first one to get five counters in a row.

### Required Materials

Materials to Gather

Materials to Copy

• Five in a Row Addition and Subtraction Stage 6 Gameboard

### Launch

• Groups of 2
• Give each group a gameboard, 2 paper clips, and two-color counters.
• "We are going to learn a game called Five in a Row. Let’s play a round together."
• Display the game board.
• “First I need to pick two numbers to add from the grey rows. I put a paper clip on one number in the top row and one number in the bottom row. Then I add them together.”
• Pick two numbers and add them.
• “The value of my sum is _____. Now I look for the number on the gameboard and cover it with a counter. Then it is my partner’s turn.”
• “My partner can only move one of the paper clips. Then they must find the sum of the two numbers.”
• If needed, select a student volunteer to be Partner B to show the steps.
• “Before you begin, you and your partner need to decide who will use the red side of the counters, and who will use the yellow side. Then take turns moving one paper clip and adding the numbers. The first person to get five counters in a row on the game board wins. The counters can be in a row across, up and down, or diagonal.”

### Activity

• 12 minutes: partner work time

### Activity Synthesis

• Display a game board with the center column covered with red counters except for the 33 at the bottom.
• Show that one paper clip is on 8.
• “This is my game board. Where would you put the other paper clip? (I would put it on 25 since $$25 + 8 = 33$$ and then you could cover the last number in the column and have five in a row.)

## Lesson Synthesis

### Lesson Synthesis

“Today, we played games that helped us practice adding within 100.”

“How did you and your partner work together during centers? What went well? What can we continue to work on?”