In this activity, students classify units of measurement by the attribute they measure: length, volume, and weight or mass. It gives students an opportunity to activate what they learned in prior grades about what different units measure.

Students may think of volume solely in terms of the number of cubic units that fit in a three-dimensional figure. They may not recognize cups, quarts, gallons, liters, and milliliters as units of volume but as a separate set of units for measuring amounts of liquids or fine-grained solids. Clarify that these units still measure how much a three-dimensional region is filled.

Invite students to share the units that they placed in each category, and discuss any disagreements. Make sure that students understand that length measures distance or how long something is, volume measures capacity or how much it takes to fill a three-dimensional region, and weight measures how heavy something is.

If time permits, consider asking students to share a few examples of units of length, volume, and weight that they have used or encountered outside of class.

In this activity, students are prompted to cut a string that is as close as possible to an assigned unit of length without using a measurement tool. The task offers an opportunity to assess students’ prior knowledge of standard units of length and to find out the kinds of objects that students already use as benchmarks for estimating length units.

As students work, listen for any benchmark comparisons that they make. For example, a student might say that an inch is approximately the length of their thumb, or a yard is approximately the length of their arm.

Some students who are assigned the length of 1 meter are likely to say that it is basically the same as 1 yard. This is acceptable during group work but should be addressed during whole-class discussion.

Students are likely to produce their length of string pretty quickly. The majority of the time in this activity will be spent comparing and discussing the estimated lengths with the whole class.

Gather and sort the strings based on their assigned length. Then display each group of strings for all to see and compare. Start with the strings estimated to be 1 foot long, followed by 1 inch and 1 centimeter. For the shorter lengths, glue or tape them to a colored piece of paper, so they can be held up for all to see.

Discuss the following:

• “How close are these estimates to each other?”
• “How close are these estimates to the actual length?”
• “What strategies were used to make estimates?”

Highlight any benchmark comparisons that students made previously, but it is not necessary to discuss other benchmarks that students did not mention themselves.

Finally, hold up both the yardstick and the meter stick to compare their actual lengths. Ensure that students notice that 1 meter is slightly longer than 1 yard. Then hold up all the strings that were assigned to be 1 yard or 1 meter. Discuss how the estimated lengths compare to the actual 1 yard or 1 meter. Ask students whether or how the strings should be re-sorted based on the given information.

This activity is intended to further ground students’ familiarity with measurement units in benchmark objects. Students are given cards with pictures of objects and asked to match each object with the closest unit of length, volume, or weight or mass.

Students may not readily distinguish between units that are very close (such as 1 liter and 1 quart) and may consider them interchangeable. This is acceptable at this point and will be investigated further in the next lesson.

When students have completed the matching, they form new groups to analyze the matches made by one of the original groups. Those who are analyzing someone else’s work can voice their support or disagreement with the placements of the cards. One student—who now belongs to a new group but whose work with the original group is being analyzed—can defend the matching decisions to the others. As they analyze and discuss one another’s work, students practice constructing logical arguments and critiquing those of others (MP3).

When most groups have finished matching the objects with the units, instruct them to form new groups based on their assigned number or letter (so that each new group consists of one person from each original group). Assign each new group a set of matched cards (done by an original group) to analyze. Display and read aloud the following guiding questions:

• “Did your original groups match the objects to the same units?” 
• “Which objects did your groups match differently?” 
• “Which objects or units were the easiest to match? Why?” 
• “Which objects or units were the hardest to match? Why?” 

Observe whether any object or unit was matched incorrectly by most of the class. If so, discuss what the correct match is.

At the end of the discussion, consider asking students to mix up the cards and put them back in the envelopes for another class to use.