In IM Grades 2 and 3, students studied some attributes of two-dimensional figures. In a previous unit, they investigated lines, rays, and segments, and drew and measured angles. They learned what it means when two lines or segments are parallel and perpendicular.

In this lesson, students use these understandings to examine attributes of two-dimensional shapes and sort the shapes into categories. As long as students can explain their rationale, they may choose to categorize the shapes using any attribute or combination of attributes—for instance, by the number of sides or angles, measurement of sides or angles, presence of parallel or perpendicular lines, and so on. Although each activity is designed to be open-ended, monitor for students who look for ways to describe or sort their shapes based on the presence or absence of angles of a specified size (right, obtuse, acute), parallel sides, or perpendicular sides. These attributes will be explored more in upcoming lessons.

This unit will continue to introduce new vocabulary to students. Students should be encouraged to add to their portable word walls throughout the unit to support successful acquisition of geometry terms.