Lesson 15

This warm-up prompts students to compare four equations. It gives students a reason to use language precisely (MP6). It gives the teacher an opportunity to hear how students use terminology and talk about characteristics of the items in comparison to one another. During the synthesis, ask students to explain the meaning of the equal sign in their reasoning.

• Groups of 2
• Display the image.
• “Pick one that doesn’t belong. Be ready to share why it doesn’t belong.”
• 1 minute: quiet think time

• 2–3 minutes: partner discussion
• Record responses.

• “What does each equation help us know about the equal sign?” (It shows us that the equal sign means the amount on either side is the same.)

The purpose of this activity is for students to make sense of a problem before solving it by familiarizing themselves with a context and the mathematics that might be involved (MP1). Students are asked to tell a story about an image in order to generate observations that lead them to ask mathematical questions about the context. This sets them up for Activity 2 in which students will be solving story problems in the given context.

• Groups of 2
• “Use numbers to describe the image.”
• 1 minute: quiet think time
• 2 minutes: partner discussion
• Share responses.

• “Think about the mathematics in this image. What mathematical questions could be asked about this picture?” 
• 3 minutes: independent work time
• 2 minutes: partner discussion
• Monitor for students who are asking questions about how many altogether or how many more or fewer.

• Invite several students to share one question with the class. 
• Record responses.
• If needed, ask, “Can this question be answered by the image? How do you know?”
• “What do these questions have in common? How are they different?” (Some of them use the same numbers. Some ask to find the total and others ask to find the difference.)

The purpose of this activity is for students to solve a variety of story problems and write addition and subtraction equations that match those problems. Students solve Put Together/Take Apart, Total or Addend Unknown problems and Compare, Difference Unknown problems. Students may solve in any way they want and write equations to match the story problem, putting a box around the number that represents the answer (MP2).

• Groups of 2
• Give students access to connecting cubes or two-color counters.

• “You will solve problems about the picture from the warm up. The questions may include some of the questions you asked. Show your thinking using drawings, numbers, or words. Write an equation to match the story problem. If you can, write two different equations that match the problem.”
• 6 minutes: independent work time
• 4 minutes: partner discussion
• Monitor for students who solved using drawings, can clearly explain how they solved, and wrote an equation.

• Display: Elena has 4 pattern blocks. Tyler has 6 pattern blocks. How many fewer patterns blocks does Elena have than Tyler?
• “How did you solve this problem? What equation did you write?”
• Record student methods and equations.
• Repeat for the other problems with the same numbers.
• “How are these problems the same? How are they different?” (They both have Elena and Tyler. They both have 4 and 6. In one we find the difference and in the other one we find the total. The answers are different.)
• If needed, ask, “Is the total important to solving the first problem? Why or why not?” (No, because we are comparing the students.)

The purpose of this activity is for students to choose from activities that offer practice adding and subtracting within 10. Students choose from any stage of previously introduced centers.

• Capture Squares
• Shake and Spill
• What’s Behind My Back

• Gather materials from previous centers:
  • Capture Squares, Stage 1
  • Shake and Spill, Stages 3 and 4
  • What's Behind My Back, Stage 2

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

• Invite students to work at the center of their choice. 
• 10 minutes: center work time

• Using a tower of 8 cubes, break the tower and hide one part behind your back.
• “What’s behind my back? How do you know?”
• Write equations to match student methods.