The purpose of this activity is for students to identify defining and nondefining attributes of rectangles and squares. Students begin by noticing what is the same about four rectangles (one of which is a square). As they notice, they identify some defining attributes (four sides, four square corners, pairs of sides that are the same length). Then given nonexamples of rectangles, students notice what makes the nonexamples different from the examples. Some, but not all, of the attributes students mention will be defining attributes. For example, students may notice that a rectangle has two long sides and two short sides, but this isn't a defining attribute.

In the Activity Synthesis, students identify squares and rectangles from their card set and the teacher supports students in developing statements about the defining attributes of these shapes. This gives students an opportunity to use language precisely to distinguish squares and rectangles (MP6).

• “What did you notice about the squares? What is the same about them?”
• “What makes the ‘not squares’ different from squares?”
• Give each group a set of shape cards from previous lessons.
• “Work with your partner to sort your shape cards into the categories of ‘rectangles,’ and ‘not rectangles.’”
• Share responses.

The purpose of this activity is for students to draw rectangles and squares. Students use dot paper to draw the shapes. As they draw, they attend to the attributes of rectangles and squares. Students also draw shapes that are not rectangles or squares. They may use the shape cards to visualize and draw shapes.

The dot paper is included in the student book. A blackline master is also attached if more dot paper is needed.

• Display the chart of student-drawn shapes.
• “Which shapes are rectangles and which shapes are not rectangles? How do you know?” (Rectangles have 4 sides and 4 square corners.)
• Circle each rectangle students identify.
• When students identify the square, ask:
  • “How many sides does it have?” (4)
  • “How many corners does it have?” (4)
  • “Is a square an example of a rectangle?” (Yes, because it has 4 straight sides and 4 square corners.)