Lesson 18

The purpose of this Number Talk is to elicit strategies and understandings students have for adding and subtracting multiples of ten. 

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

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

• “How are \(32 + 10 + 10\) and \(32 + 20\) the same and different?” (Both equal 52. Both expressions have 32 as an addend. In one expression, the tens are separate and in the other, it shows 20.)

The purpose of this activity is for students to learn a new center called Get Your Numbers In Order. Students use their understanding of relative magnitude to order numbers. They take turns placing two-digit numbers on the board and must make sure that the numbers across the board go from least to greatest. If a number cannot be placed on the gameboard, students say “pass” and get 1 point. Then it is their partner’s turn. The player with the fewest points when all the boxes on the board are filled is the winner. Students should remove the cards that show 10 before they start.

• Put each gameboard in a sheet protector.

• Groups of 2
• Give each group a set of cards, a gameboard, and a dry erase marker.
• “We are going to learn a new center called Get Your Numbers In Order.”
•  Display the gameboard and number cards.
• “When it is your turn, choose two cards and make a two-digit number. The first person writes their number on the gameboard, anywhere they would like. The next person chooses two cards and makes a two-digit number. That number can be written on the board if there is a space where it fits. All of the numbers across the board must be in order from least to greatest. If you cannot write your number on the board, you get one point. The person with the fewest points when the board is filled is the winner.”
• Demonstrate playing a couple rounds with the class. 
• “Now you will play with your partner.”

• 10 minutes: partner work time

• Display a gameboard with all but one space filled in. 
• “What numbers could we put in this space that would keep the numbers in order?”

The purpose of this activity is for students to choose from activities that focus on counting, comparing, and writing two-digit numbers.

Students choose from any stage of previously introduced centers.

• Greatest of Them All
• Grab and Count
• Write Numbers

• Gather materials from previous centers:
  • Greatest of Them All, Stage 1
  • Grab and Count, Stage 2
  • Write Numbers, Stages 1 and 2

• Groups of 2
• “Now you will choose from centers we have already learned.”
• Display the center choices in the student book.
• “Think about what you would like to do first.”
• 30 seconds: quiet think time

• Invite students to work at the center of their choice.
• 8 minutes: center work time
• “Choose what you would like to do next.”
• 8 minutes: center work time

• “What is one thing you learned or got better at by working on the activity you chose?”