Lesson 7

The purpose of this Number Talk is to elicit the ways students look for to use the structure of two-digit numbers to subtract (MP7). These understandings help students develop fluency and will be helpful later in this lesson when students will need to be able to find the difference between the estimate and actual measurement of an object.

• 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 could you use \(37-20\) to help you with \(37 - 21\)?”

The purpose of this activity is for students to learn stage 2 of the Estimate and Measure center. Students estimate and measure the length of objects. This stage includes centimeters, inches, and feet. Students should only measure in centimeters at this point in the unit. In this activity, students also find the difference between their estimate and their measurement for extra practice.

• Gather or identify objects of various lengths (pencils, markers, books, glue, scissors, shoe, tape dispenser, side of desk, length of bulletin board).

• Groups of 2
• Give students access to centimeter rulers and meter sticks.
• Give each student a recording sheet.
• “We are going to learn a new center called Estimate and Measure. Today we are going to estimate and measure the length of different objects.”
• “First you and your partner will decide on an object in the room to measure. Then you will decide what tool you will use to measure the object.”
• Choose an object to measure and hold it up for students to see.
• “What tool would you use to measure this object?”
• “Before measuring the object, you and your partner will both estimate the length of the object using the unit you chose. Your estimates do not have to be the same. Record your estimate.”
• Demonstrate estimating the length of your object and recording it on the recording sheet.
• “Now work with your partner to measure the object and record the actual measurement.”
• Demonstrate measuring the object, thinking aloud as you line up the endpoints and use the number on the tool to determine the length.
• Record the actual measurement on the recording sheet.
• “If you have time: Once you have estimated and measured the object, find the difference between your estimate and the actual length.”
• Demonstrate finding the difference.
• “Put your object back and choose another object to measure.”

• 10 minutes: partner work time

• Display a row of the recording sheet with this information:
  • Object: notebook
  • Estimate: 20 cm
  • Actual Measurement: 31 cm
• “How can we find the difference?” (We can add on to 20 until we get to 31. We can subtract 20 from 31.)

The purpose of this activity is for students to choose from activities that focus on measurement or story problems. Students choose from any stage of previously introduced centers.

• Estimate and Measure
• Math Stories

Gather materials from:

• Estimate and Measure, Stage 2
• Math Stories, Stage 5

• “Now you will choose from centers we have already learned. One of the choices is to continue with Estimate and Measure.”
• 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 did you like about the activity you worked on today?”