2.8.C
The Standard
classify and sort polygons with 12 or fewer sides according to attributes, including identifying the number of sides and number of vertices
Texas Essential Knowledge and Skills for Mathematics
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students examine closed shapes with straight sides and count each side and vertex. They group polygons by shared counts and explain the rule they used.
What Mastery Looks Like
- Students accurately count sides and vertices on regular and irregular polygons. They sort shapes by a clear rule and explain each placement using those counts.
Common Misconceptions
- Students may count curved edges as sides or confuse sides with vertices. They may double-count the starting vertex or think turning a shape changes its type.
How to Assess It
- Give students six polygon cards with 3 to 12 sides. Ask them to record each card’s sides and vertices, then sort the cards using a stated rule.
Lesson moves
Ways to Teach It
Students build polygons with craft sticks, label the vertices, and arrange the shapes from fewest to most sides.
Show two different-looking hexagons and ask, “How can you prove both belong in the same group?”
Play Shape Sort Relay using polygon cards labeled only with letters, then have teams state and defend their sorting rule.
Photograph signs, tiles, and windows around school, then have students classify each polygon outline by its number of sides.
Keep exploring
Related Standards
- 2.8.A
create two-dimensional shapes based on given attributes, including number of sides and vertices
- K.6.E
classify and sort a variety of regular and irregular two- and three-dimensional figures regardless of orientation or size
- 1.6.A
classify and sort regular and irregular two-dimensional shapes based on attributes using informal geometric language
- 2.8.B
classify and sort three-dimensional solids, including spheres, cones, cylinders, rectangular prisms (including cubes as special rectangular prisms), and triangu...
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