I start this lesson by reading “The Greedy Triangle”. I like to use this book to begin this lesson because it discusses the number of sides for the various plane shapes. The book points out some of the many frequent places where 2D shapes can be found.
One of the misconceptions for the standard G.A.1 is that students will incorrectly count the number of sides or vertices. To help overcome this misunderstanding, during the read aloud I stop frequently to count the sides and the vertices of the shapes.
After reading the book, I hold up some 2D shapes and we talk about their names and count the number of sides and vertices. I hand out white boards and markers to each student. I call out the name of a shape and the students will draw the shape on their white board. I do this as a review of 2D shapes.
I then demonstrate how to build a triangle using pipe cleaners and straws. Students will be able to make concrete connections with the number of sides and vertices. I like to use pipe cleaners and straws because when the students build the shapes, the pipe cleaners provide a distinct, concrete representations for the sides and vertices of the shapes (MP4).
I hand out a bag of straws and pipe cleaners to each student, and we build a triangle together. As a group we discuss the properties of each shape (number of sides, number of vertices, if the sides are equal or not and if the sides are curved or straight). I discuss the prefixes of each shape name and how it relates the number of sides. Students will then be able to make the connection that the name of the shape is actually referring to the number of sides of the shape.
Students will use their straws and pipe cleaners to make the shape on their worksheet: Geometry-Straw Shapes.docx. They will list the number of sides and vertices, and draw an everyday object that is representative of that shape.
To close out the lesson, I instruct students to get their math journal and draw an octagon, a shape with 8 sides, and label the vertices and sides.