Lesson objective: Understand that angles and sides are defining attributes of shapes.

Students bring prior knowledge of defining attributes from 1.G.A.1. This prior knowledge is extended to include angles as students sort shapes by defining attributes. A conceptual challenge students may encounter is understanding that not all attributes are defining attributes (such as size or color).

The concept is developed through work with a variety of shapes in multiple orientations, which supports students' understanding that defining attributes do not change regardless of the size, color, or orientation.

This work helps students deepen their understanding of equivalence because students are making connections between number of sides/angles and the shape they define.

Students engage in Mathematical Practice 3 (Construct viable arguments and critique the reasoning of others) as they articulate how their shapes are sorted into the groups and discuss with other students how their solutions are similar or different.

**Key vocabulary:**

**Special materials needed:**

- attribute blocks (optional)
- glue
- scissors
- task handout