Lesson 12

Center Day 2 (optional)

Warm-up: Number Talk: Differences (10 minutes)


The purpose of this Number Talk is to elicit strategies and understandings students have for subtracting a one-digit number from a two-digit number by using a ten. When students decompose a number to lead to a ten, they look for and make use of the structure of whole numbers and the properties of operations (MP7).


  • 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.

Student Facing

Find the value of each expression mentally.

  • \(17 - 7\)
  • \(17 - 9\)
  • \(15 - 5\)
  • \(15 - 8\)

Student Response

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Activity Synthesis

  • “How can we use the first expression to find the value of the second one?” (I knew that \(17 - 7 = 10\), and then I took away 2 more.)

Activity 1: Revisit Sort and Display (20 minutes)


The purpose of this activity is for students to learn stage 2 of the Sort and Display center. Students sort 20–30 objects into 3 categories and make a picture or bar graph that shows how they sorted. Then, they ask their partner 2 questions that can be answered based on their graph. Students are given an opportunity to sort items, represent how they sorted, and create questions that can be asked about the data in their representation (MP2, MP6).

To connect this center to English Language Arts, students could use books to find a collection. Students look at the cover of a book and choose 3 words or 3 images they think will show up most often in the story and explain why to their partner. Partners record these choices as initial categories. Students then read or look through the book together, explore their prediction and decide together if they want to revise their categories based on what they’ve read. On the second read, they collect and record data for their revised categories. Lastly students create representations based on their data and write 2 “How many?” questions that can be asked about the data in their representations.

Required Materials

Materials to Gather

Materials to Copy

  • Sort and Display Stage 2 Recording Sheet

Required Preparation

  • Each group of 2 needs a collection of 20–30 objects that could be sorted into at least 3 categories. Examples: pattern blocks, cubes, sets of books, or a combination of blocks, cubes, and counters.


  • Groups of 2
  • Give each student a recording sheet.
  • “There is a new center called “Sort and Display.”
  • Read directions aloud to students.
  • “Choose a collection to sort. Sort into 3 categories. Represent the data in a graph that shows how many are in each category.”
  • “After you’ve made your representation, you and a partner should ask each other questions about the data in your graph.”


  • 12–15 minutes: partner work time
  • Monitor for 12 graphs to share in the activity synthesis.

Activity Synthesis

  • Display student representation.
  • “What questions can we ask about the representation of how they sorted?”

Activity 2: Centers Choice Time (20 minutes)


The purpose of this activity is for students to choose from activities that focus on adding or subtracting.

Students choose from any stage of previously introduced centers.

  • What's Behind My Back?
  • How Close?
  • Number Puzzles

Required Preparation

Gather materials from :

  • What's Behind My Back, Stages 2 and 3
  • How Close, Stages 13
  • Number Puzzles, Stages 1 and 2


  • “Now you will choose from centers we have already learned that focus on adding and subtracting.”
  • 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.
  • 15 minutes: center work time

Student Facing

Choose a center.

What's Behind My Back?

Center. What's Behind My Back.

How Close?

Center. How Close.

Number Puzzles

Center activity. Number Puzzles.

Activity Synthesis

  • “Which activity did you choose? What did you like about the activity you chose?”

Lesson Synthesis

Lesson Synthesis

“Today we chose activities to work on and worked with a partner during center time.”

Math Community

Display chart from previous lesson and read the norms to students.

“What went well? What can we continue to work on?”