In the previous activity, students started to think about how to measure distances in different situations. The activity introduces the context of designing a course for a 5K fundraising walk. Students will continue working with this context in future lessons. In this activity, they come up with a method for measuring the walking distance of a path that is too long to measure with a measuring tape. As students select appropriate strategies to measure distances, they have the opportunity to consider the limitations and benefits of each tool when measuring (MP5).

Check in with each group about their method of measurement. When they have a plan that they understand, they can move to the next activity.

In this activity, students use the method they came up with in the previous activity to measure the length of a path chosen by the teacher. 

In this group activity, students take turns sharing their initial ideas and first drafts. As students trade roles explaining their thinking and listening, they have opportunities to explain their reasoning and critique the reasoning of others (MP3). As students revise their writing, they have an opportunity to attend to precision in the language they use to describe their thinking (MP6).

It is not important that students’ results are very accurate. They will measure the distance again with a trundle wheel in a later lesson. The main point of this activity is to think about measurement methods and to discuss the advantages and disadvantages of different methods.

Use Stronger and Clearer Each Time to give students an opportunity to revise and refine their response to the last question, about the advantages and disadvantages of each group’s method. In this structured pairing strategy, students bring their first draft response into conversations with 2–3 different partners. They take turns being the speaker and the listener. As the speaker, students share their initial ideas and read their first draft. As the listener, students ask questions and give feedback that will help their partner clarify and strengthen their ideas and writing.

If time allows, display these prompts for feedback: 

• “ makes sense, but what do you mean when you say. . . ?”

• “Can you describe that another way?”

Close the partner conversations and give students 3–5 minutes to revise their first draft. Encourage students to incorporate any good ideas and words they got from their partners to make their next draft stronger and clearer. If time allows, invite students to compare their first and final drafts. Select 2–3 students to share how their drafts changed and why they made the changes they did.

After Stronger and Clearer Each Time, invite the different groups to share their solutions. Ask them to:

• Compare how close their answers are.
• Compute the approximate relative error (difference/total length).
• Discuss the advantages and disadvantages of their methods and sources of discrepancies in their measurements, and how a small error can propagate. ​

The takeaway should include:

• Proportional reasoning can be used to find longer distances. If it is known that it takes 10 steps to walk 8 meters, then it will take 20 steps to walk 16 meters.
• Small errors can magnify over longer distances.
• Methods were either not very precise (prone to introduce error), or they were precise but cumbersome to implement.