The purpose of this activity is to encourage students to observe attributes of shapes and use them to sort shapes into groups. When students sort the cards, they look for common attributes or structures shared by different shapes (MP7). Students notice that there are multiple ways to categorize the shapes and that a shape may belong to more than one category depending on the attributes used to sort.

In grade 2, students refer to right angles as square corners. In this activity, students learn to use the terms angle in a shape and right angle in a shape to describe the corners of shapes. Note that the term “angle” is understood informally and used only in reference to shapes and their geometric attributes (for instance, students distinguish squares from other rhombuses). They will not learn the formal definition of an angle—a figure made up of two rays that share the same starting point—or that it is a measurable attribute until grade 4.

When students consider the language they use and revise it to describe a shape in detail or with more specificity, they attend to precision (MP6).

The cards in this activity will be used again in centers.

• Invite 1–2 previously selected groups to share any new categories during their partner work time. Record any additional attributes used to sort the shapes.
• “What words or phrases were helpful for describing the shapes?” (four, five, side, corner, length, equal, triangle, square, rectangle, pentagon, hexagon)
• Display Card O.
• “The part of the shape made by two straight sides that meet is called an angle in the shape. How many angles does this shape have?” (Shape O has 4 angles.)
• “This shape also has two special angles. Their sides join in a way that forms a right angle in the shape. This is the way that sides meet in a square and in rectangles. What other shapes have right angles?” (B, F, M, and S)