The purpose of this activity is for students to sort triangles into more specific categories. This requires students to attend to an attribute other than the number of sides. As students sort the triangles, monitor for students who sort by the number of equal side lengths or the presence of a right angle (MP7). Although the terms “equilateral,” “isosceles,” and “scalene” are not introduced in this lesson, it is fine if students already know them and use them to describe the groups of triangles.

• Invite groups to share their categories and how they sorted their cards.
• Allow as many categories to be presented as time permits, but be sure to highlight categories based on the number of sides with equal length.
• Highlight the use of terms such as “equal side lengths” and “angles.”
• Record and display the attributes students use to categorize the triangles.

The purpose of this activity is to sort quadrilaterals by their attributes. By now students may be inclined to look for sides of equal lengths and right angles. They may not look for parallel sides (and are not expected to know the term “parallel”), but may notice that some quadrilaterals have pairs of sides that are oriented in the same direction (MP7). Encourage students to describe such observations in their own words.

The quadrilateral cards from this activity will be used in the next lesson and in centers.

• “Display your sorted cards so that others can see them.”
• “Visit another group’s cards and see if you can figure out how they sorted their quadrilaterals. Be prepared to share your reasoning.”
• 2–3 minutes: Students visit other groups’ displays.
• Invite each group to share how the cards were sorted and their reasoning. Record and display the attributes students use to categorize the quadrilaterals.
• Attend to the language that students use to describe the categories and shapes, giving them opportunities to describe the shapes more precisely.
• Highlight the use of terms such as “equal sides” and “right angles.”