Lesson 3

This warm-up prompts students to compare four shapes. It gives students a reason to use language precisely (MP6). It gives the teacher an opportunity to hear how students use terminology and talk about characteristics of two- and three-dimensional shapes.

• Groups of 2
• Display the image.
• “Pick one that doesn’t belong. Be ready to share why it doesn’t belong.”
• 1 minute: quiet think time

• “Discuss your thinking with your partner.”
• 2–3 minutes: partner discussion
• Share and record responses.

• “Let’s find at least one reason why each one doesn’t belong.”
• “What solid shapes do the images for A, B, and C show?” (cube, cone, and cylinder)
• “Does D show a solid shape? Why or why not?” (Maybe it is supposed to be a sphere. It looks like it is just a circle.)
• “A circle is not one of our solid shapes. We call it a flat shape.”

The purpose of this activity is for students to sort two-dimensional shapes into categories that make sense to them. As students sort, they may sort by defining attributes such as number of sides or corners. Some students may sort by the name of the shape. Somes students may sort by non-defining attributes such as color or size. Students may have leftover shapes depending on how they sort. As students work, encourage them to refine their descriptions of the shapes using more precise language and mathematical terms (MP6). Students' sorts are displayed for the gallery walk in the next activity.

• Create a set of Flat Shape Cards from the blackline master for each group of 2. 

• Groups of 2
• Give each group a set of shape cards.

• “With your partner, sort your shape cards into groups. Give each group a category. Remember, a category is a label that tells how objects in a group are alike. Explain each category you made. Then sort the cards in a different way.”
• 10 minutes: partner work time
• Consider asking:
  • “How might you describe this shape?”
  • “Why did you place this shape in this group?”
  • “Why didn’t you place _____ with this group?”

• “What words did you use to explain how you sorted the shapes?” (Number of points, sides, corners, name of shapes)
• Highlight the use of terms like triangle, circle, rectangle, square, hexagon, corners, and sides.

The purpose of this activity is for students to participate in a gallery walk in which they see a variety of ways the flat shapes have been sorted. Student discuss with their partner what they notice about how their classmates sorted the shapes (MP3).

• Display each group's work from the previous activity. 

• Groups of 2
• “We are going to do a gallery walk to look at different ways we have sorted the flat shapes. Talk with your partner about what you notice about the work. See if you can tell how they sorted the shapes. Record how they sorted in your book.”

• 3 minutes: partner work time
• “Now we will all move so we can see how a different group sorted the shapes.”
• 3 minutes: partner work time
• Repeat as time permits.

• “In what different ways did we sort the shapes?”
• As each different way is mentioned, ask the group that sorted in that way to explain how they decided which shapes belonged in each category.