The purpose of this activity is to emphasize the importance of identifying the length of a unit when measuring (MP6). Students work in groups to measure the same length of string using straws. Students find and report measurements of different lengths because they are provided with straws of different lengths. In the Synthesis, students discuss that although the same length of string was measured, the measurements are different, because different length units were used. This sets students up to discuss what happens when everyone uses the same length unit in the next activity.

Straws may be replaced by pipe-cleaners or other rigid objects that can be cut to the specified lengths.

This activity uses MLR8 Discussion Supports. Advances: Listening, Representing

• “Why do you think your total number of straws is different?”
• “How can you make sure the entire length of the string was measured?”

• “How long is Priya’s string?”
• Record responses.
• “Why are our length measurements different?” (Some groups maybe didn’t line up their straws correctly. Maybe the straws weren’t the same size.)
• 30 seconds: quiet think time
• 1 minutes: partner discussion
• Share responses.
• Invite previously identified students to demonstrate their measurements.
• “Both of these groups started at the beginning of the string and lined up straws with no gaps or overlaps until they reached the end.”
• “Why are the measurements different?” (The straws are different sizes. One group used short straws and one group used long straws.)
• “The measurements are different because each group used different length units.”
• “A length unit is the length of the object you use to measure.”

The purpose of this activity is for students to understand why it is important to be precise about the length of the unit used to measure (MP6). All student groups use centimeter cubes to measure. After measuring, students compare their measurements with other groups. In the Synthesis, students discuss why each group's measurement is the same, or nearly the same, after they measured the length with cubes. Students are introduced to standard units, but do not need to use this term.

• Share and record measurements.
• “Why is every group's measurements the same, or closer to the same, length?” (They are the same because we all used the same length unit. We all used cubes that have the same length.)
• As needed, restate student responses when they say the cubes are “the same” to emphasize that the cubes have the same length.
• Display a centimeter cube and a connecting cube.
• “If some groups used these cubes and other groups used connecting cubes, would our measurements have been the same? Why?” (It would not be the same because the cubes are not the same length.)
• “Straws and cubes can be confusing to use as length-units because they can be lots of different sizes.”
• “There are units that people around the world use to measure that always have the same size. They are called standard units.”