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Characteristics of Polygons
Students will be able to categorize polygons by attributes.
- Tell students that today they are going to be exploring shapes and their attributes. Explain that attributes are characteristics or features of something.
- Give examples for attributes using people or items that the students can all see. Say, "Some of the attributes I could use to describe myself are that I’m tall and have dark colored eyes." or "The letter V on our handwriting poster has two straight lines and is an open shape."
- Ask students to turn to a partner and describe the attributes of an object in the classroom.
- Call on a few students to share what their partner said.
Explicit Instruction/Teacher modeling(15 minutes)
- Give each student two sticky notes.
- Explain that they are going to go on a quick two minute shape search in the classroom. They will find, draw, and label a shape on each stickey note.
- Model for students how you want them to do this and provide a shape example that is less common. Say, "I see half a circle on our bulletin board. I’m going to do a quick drawing of it and label it with the name semicircle on my first sticky note."
- Tell students that it’s okay if they’re not sure what the name of a shape is and that if that happens they can just write a few words to describe it.
- Have students gather at the carpet or other meeting space once they have found their shapes or the two minutes of search time is up.
- Create a T-chart on poster paper with the titles "Polygons" and "Not Polygons."
- Ask students if they remember and can define for the class what a polygon is.
- Call on a few students to share their thinking.
- Restate for the class a clear definition of polygon: a 2D or flat, closed shape with straight sides.
- Have students come up to the T-chart and place their shapes on the correct side.
- Ask the class if they agree with where everyone placed their shapes or if they disagree to explain why they think a shape should be moved.
- Draw on sticky notes any examples that you would like the whole class to place on the chart that they missed in their shape search. For example, an open shape, an irregular polygon, or a 3D shape.
Guided Practice(15 minutes)
- Show students the Polygons Shape Sort worksheet.
- Explain that they are going to cut apart the shapes on the dotted lines and then sort them into two groups on their desk. They’ll have to decide how they want to sort them.
- Send students back to their desks with a Polygons Shape Sort worksheet.
- Call on a few students to explain how they sorted their shapes. (Students' answers could include, "I put shapes with four sides in one group and shapes without four sides in another group. I put regular looking shapes in one group and irregular shapes in another group.")
- Ask students to put all their shapes back into one group on their desk. Remind them that this is a group of polygons. Poly means many and gon means a shape with a certain number of angles. This is a group of shapes with many angles.
- Ask for a student to remind the class what a quadrilateral is. (A quadrilateral is a four sided shape.)
- Tell them to find and group all the quadrilaterals together in one group and set the other shapes to the side.
- Check that students have all the quadrilaterals grouped by listing off all the letters for them. (Quadrilaterals: A, B, E, G, I, J, L, M, N, P, R, and T)
- Explain that in the group of quadrilaterals there are other more specific groups like trapezoids. Trapezoids are four sided shapes with one set of parallel lines. Parallel lines are two lines that are always the same distance apart and never touch.
- Ask students to sort their quadrilaterals into a pile of trapezoids and not trapezoids. (Trapezoids: B, I, N, R, and T) Then, have them set the shapes that are not trapezoids to the side.
- Ask students for ideas of how they could categorize the remaining shapes.
- Tell them that now you want them to sort the shapes into rectangles and not rectangles. Remind them that rectangles have exactly two sets of parallel lines and four right angles. Show students how they can use the corner of a standard piece of paper or an index card to check if a shape has a right angle. (Rectangles: E, J, L, and M) Then, have them set the shapes that are not rectangles to the side.
- Finally, ask if there is one final way to sort the remaining shapes. Offer squares and not squares if a student does not suggest it. Remind students that a square has exactly four equal sides and four right angles. (Squares: E, and J)
- Ask students to describe what happened to the number of shapes as attributes were added. (The number of shapes in the group decreased.)
Independent working time(15 minutes)
- Give each student a piece of white construction paper and a ruler.
- Tell them they are going to use a ruler to draw a picture made up of polygons. For example, robots, animals, and a classroom.
- Explain that their drawing must contain a variety of polygons and that they have to label at least eight of the shapes.
- Preteach key terms.
- Have students sort shapes in partners instead of individually.
- Have students include a variety of challenging polygons in their drawing (septagon, nonagon, etc.) and other geometric terms (parallel lines, open shape, cube etc.).
- Give students the Categorizing Shapes Check worksheet to complete as a formative assessment.
- Have students compare their answers with a partner and discuss any differences with each other, before sharing them as a whole class. Clarify any misunderstandings.
Review and closing(2 minutes)
- Do a gallery walk, so that students can see the polygon pictures their classmates created.
- Invite students to discuss their observations and opinions of the polygon pictures.