Direct students’ attention to the reference created using Collect and Display. Ask students to share their process for measuring the path. Invite students to borrow language from the display as needed, and update the reference to include additional phrases as they respond.

Ask each group to report their measurement for the length of the path and record their answers for all to see. Guide students to compare these answers by asking questions like these:

• “Do all of these answers seem reasonable? Do any of these answers seem unreasonable? Explain your reasoning?”
• “Why are these answers not all exactly the same? What are some sources of error?” (Not going in a straight line, the wheel wobbles, the ground is uneven, only counting number of clicks but not parts of rotations, etc.)
• “What units did you use? What units would be most convenient for designing the course of a 5K walk-a-thon?” (Metric since we are designing a 5 kilometer course.)
• “What degree of precision is appropriate to report?" (To the closest 1 meter at most. Reporting in centimeters or milimeters for such long distances using a tool like a trundle wheel would imply a degree of precision that would not be appropriate.)

If time permits, consider asking, “If you could choose your own diameter for a trundle wheel, what would it be?” (A diameter that creates a circumference of 1 meter would be convenient, about 32 centimeters.)

Collect and store students’ trundle wheels so they will have access to them again in the next lesson.

If students lose track of the number of rotations along the path, consider asking:

• “Explain how your trundle wheel helps you measure distance.”
• “How can you use your team to help you keep track of the number of rotations?”