I begin this lesson by reading the book “The Greedy Triangle”. I like to use this book because it demonstrates the transformation of the triangle to other polygons based on the addition of essential attributes (sides and vertices). While reading the book, I have students come up and count the vertices of the shapes.
If the book isn't available, there is a YouTube version.
In this video, a student is counting the sides and vertices on a square.
I then display a trapezoid and a hexagon. Have children share their observations about each shape. Then ask questions to generate discussion about ways these shapes are alike or different from other shapes. For example:
Exploring the attributes of shapes is a first step in developing geometrical ideas. As I work through this lesson, I help children relate what they are learning to the world around them. I like to ask where they have seen squares, rectangles, triangles, and circles outside of school, and how those shapes are like the shapes in their math lessons. Geometry builds on children’s spatial sense, and many children who struggle with arithmetic may find the mathematics of geometry much more satisfying and interesting! I like to take advantage of this and get students excited and involved who otherwise tend to disengage during math.
One of the common student misconceptions in describing the attributes of geometric shapes (1.G.A.1) that I have found is that students may identify only the vertices on the trapezoid that have acute angles. Remind children that a vertex feels like a point, but it is still a vertex even if it is less pointy. A vertex is the point where two sides of a polygon meet, so in the case of a trapezoid, two vertices are very pointy and the other two are not as pointy. I want to drive this point home with students to nip this misconception in the bud.
Then I hand each student some pattern blocks and give the following directions to the class:
Sort two-dimensional shapes into two groups. One group should have shapes that are curved. The other group should have shapes with straight sides.
After students have sorted their shapes, I ask the following questions:
After children complete their work, I have volunteers share their observations.
Using the Describe 2D shapes.ppt, I work through the first slide together and say the names for trapezoid and hexagon as I define these shapes with children.
I then have children complete the first few questions on their worksheet. I ask the following question afterwards:
Finally, I have students finish the remainder of the Describe 2D shapes_worksheet.docx on their own.
Most of my students were successful in producing high quality work in this lesson. One way I ensured success was by allowing my lower students to use manipulatives - pattern blocks. These seemed to help them in counting the number of sides and vertices on the shapes by providing them with a concrete example to help them in drawing the shape and actually touching the sides and vertices while counting them. Eventually, I want them to be able to see the shape mentally and be able to come up with the sides and vertices without the manipulatives, but, for now, it's good to give them the support they need until they can make that mental leap.
To close out this lesson, I have students draw a rectangle or square in their math journal and label the sides and vertices.