Measuring with Different-Size Units

5 min

Teacher Prep
Setup
Quiet think time, then provide access to blue (9-cm) and dark green (6-cm) Cuisenaire rods, or small and large paper clips.
Required Preparation
Prepare to display or distribute paper clips in two sizes: regular and jumbo.

Narrative

Students begin by thinking about length in terms of non-standard units—a regular paper clip and a jumbo paper clip—and consider how the size of units affects the number of units needed to express a length.

Some students may be able to reason that it takes more of the smaller unit than the larger unit to measure the same length. Encourage them to articulate their reasoning. Others may need to visualize the situation by drawing or by measuring with actual paper clips.

Launch

Hold up a regular paper clip and a jumbo paper clip for the students to see. Give them 1 minute of quiet think time. Afterward, allow students to use the paper clips to measure the paper if they need or wish to do so.

Student Task

This picture shows paper clips in two sizes: regular and jumbo.

Does it take more regular or jumbo paper clips lined up end to end to measure the width of a piece of printer paper? Be prepared to explain how you know.

Sample Response

It takes more regular paper clips, because they are shorter than jumbo paper clips.

Activity Synthesis (Teacher Notes)

Ask students to share their responses and reasoning. Highlight the fact that it takes more of a smaller unit and fewer of a larger unit to measure the same length.

Anticipated Misconceptions

Some students may assume that it will take more of the longer clips because they are used to associating the idea of “more” with “larger.” Encourage them to use the manipulatives to see that it actually takes fewer of the longer clips to reach across the paper.

Standards
Building On
  • 2.MD.2·Measure the length of an object twice, using length units of different lengths for the two measurements; describe how the two measurements relate to the size of the unit chosen.
  • 2.MD.A.2·Measure the length of an object twice, using length units of different lengths for the two measurements; describe how the two measurements relate to the size of the unit chosen.
Building Toward
  • 6.RP.3.d·Use ratio reasoning to convert measurement units; manipulate and transform units appropriately when multiplying or dividing quantities.
  • 6.RP.A.3.d·Use ratio reasoning to convert measurement units; manipulate and transform units appropriately when multiplying or dividing quantities.

30 min