Lesson 1

The purpose of this warm-up is to invite students to share what they know about inches. Later in the lesson, students will explore lengths that are not a whole-number of inches.

• Display the question.
• “What do you know about inches?”
• 1 minute: quiet think time

• Record responses.

• “Inches are a unit we use to measure length. What are some lengths that we could use inches to measure?“ (The length of a shoe. The length of material for an art project. The height of a desk.)

In grade 2, students only measured the length of objects that were whole units and sometimes described lengths as “about 4 inches.” The purpose of this activity is for students to learn that fractions of an inch can be useful for measuring the length of an object that is not exactly a whole number of inches.

Given a ruler marked with inches, students measure objects around the room. They may record measurements in whole inches even for objects whose length is not exactly a whole number inches. In the synthesis, discuss the need for fractions of an inch to describe lengths more precisely (MP6). 

The rulers from this activity are used in the next activity.

• Make copies and cut out the rulers from the blackline master (5 rulers per page). 

• Groups of 2
• Give each student a ruler.

• “Use your ruler to measure the length of objects in the room. Work with your partner. You should each choose 3 objects.”
• 5–7 minutes: partner work time
• Monitor for students who find objects that are not exactly whole numbers of inches. Highlight the objects and their measurement in the synthesis.

• Display the inch ruler and an object that wasn’t exactly a whole number of inches.
• “What is the length of this object?” (Between 3 and 4 inches. More than 3 but less than 4. Three-and-a-half inches.)
• If needed, “Could we say that the length of this object is (a whole number of) inches.” (No, It's between 3 inches and 4 inches.)
• “We need a way to make our measurements more precise. We'll think about this more in the next activity.”

The purpose of this activity is for students to partition the inches on a ruler to show half inches and then use their ruler to measure lengths to the nearest half of an inch.

The unpartitioned rulers from this activity are used in the next lesson.

• Each student needs a ruler from the previous activity.

• Groups of 2
• “How could we adjust our rulers to measure lengths that are in between whole numbers?” (We could fold each inch into smaller equal parts. We could partition each inch into halves.)

• “Work with your partner to partition every inch on one ruler into halves of an inch. Decide whose ruler you’ll partition. Leave the other ruler in whole inches.”
• 2–3 minutes: partner work time
• “Just like in the last activity, you may have objects that don't line up with one of the marks on the ruler. How might you record those lengths? Talk to your partner about it.” (Estimate how long the object is. Record the mark that is closest.)
• 1 minute: partner discussion
• Share responses.
• “Work with your partner to choose objects to measure to the nearest half inch. You should each measure 3 objects.”
• 5–7 minutes: partner work time

• “Tell me about how you partitioned the inches into halves.”
• “How could you make sure the halves are the same size?”

• “How did you measure the length of objects when the length was in between the marks on your ruler?” (We recorded the mark that was closest. The length was right between 1 inch and \(1\frac{1}{2}\) inches, so we estimated the length to be about \(1\frac{1}{4}\) inches.)

• “Save both rulers—the one you partitioned to show halves of an inch and the one that is not partitioned—for the next lesson.”