Lesson objective: Understand that the name of a shape is determined by its defining attributes and that non-defining attributes such as position, color or size do not change the name of the shape.

Students bring prior knowledge of defining attributes from K.G.A.1. This prior knowledge is extended to shapes of different sizes and in varying orientations as students look closely at triangles with different angles and positions. A conceptual challenge students may encounter is visualizing and understanding that triangles may look different but still have the same defining attributes.

The concept is developed through work with images of triangles in different sizes and orientations, which allow students the opportunity to focus on the defining attributes of the same shape, even though the shapes look different.

This work helps students deepen their understanding of equivalence because they will discover that defining attributes help to explain how triangles are the same even though they look different.

Students engage in Mathematical Practice #3 (Construct viable arguments and critique the reasoning of others) as they use their understanding of defining attributes of triangles to create an argument for their sorting rule and critique the sorting rules of others. Students will also engage in Mathematical Practice #7 (Look for and make use of structure) as they visualize the defining attributes to identify and describe triangles.

**Key vocabulary:**

- different
- same

**Special materials needed:**

- Task Triangle Cards