Comparing shapes by their sides and corners
In kindergarten, children learn to compare flat and solid shapes by describing their parts, such as how many sides and corners they have, and to say how the shapes are alike and different.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
Try these with your child
These are real questions from our kindergarten practice. Tap the speaker to hear one read aloud, or the light bulb for a hint, and talk about the answer together.
Question 1 of 3
How is a triangle different from a square?
- It has 3 sides
- It has 4 sides
- It is round
Why this matters
Talking about sides and corners moves your child from naming shapes to understanding them. In 1st grade they use these features to decide what makes a shape a triangle or a square, and in 2nd and 3rd grade to sort shapes by their sides and angles. Comparing shapes in words also builds the habit of explaining their thinking, which matters in every part of math.
Where kids can get stuck
- Counting one side twice, or losing track of where they started, and saying a square has 5 sides.
- Thinking a rectangle and a square have nothing in common, not noticing both have 4 sides and 4 corners.
- Describing shapes only by color or size, saying "the red one is bigger" instead of naming sides or corners.
How you can help
- Trace around the edges of a picture frame, a cracker, and a slice of cheese with your finger, counting the sides and corners together.
- Hold a ball and a box, and ask your child to tell you two ways they are different and one way they are alike.
- Make shapes with craft sticks or toothpicks, then compare two of them by counting the sides and talking about which sides are the same length.
If it’s helpful, you can watch the kid-friendly video below, or sign up for free, adaptive practice in Bobby's Math Club.
Kid-friendly explanation
Questions parents ask
Why does my child count the sides and corners of shapes?
Counting sides and corners helps your child understand what makes each shape what it is. A triangle always has 3 sides and 3 corners, no matter its size or position. Learning to notice these features moves your child beyond recognizing pictures to understanding shapes, which is how geometry works in later grades.
What does vertices mean?
Vertices is the math word for corners, the points where two sides meet. One corner is called a vertex. Kindergarten teachers often use both words, corners and vertices. Your child can use either one, as long as they can count and describe the corners of a shape correctly.
How is this different from naming shapes?
Naming shapes means recognizing them, such as saying "that is a triangle." This skill asks your child to explain why, by describing parts and comparing shapes. For example, your child might say a square and a rectangle both have 4 sides and 4 corners, but a square's sides are all the same length.
Make learning math fun
Bobby's Math Club turns kindergarten math practice into something fun to do together.
- Free, unlimited practice for every child in your family
- Practice that starts where your child is and grows with them
- Hints when they are stuck, and a celebration when it clicks
Written by Robert “Bobby” Barnett
Bobby is an award-winning math teacher, the author of Meet Every Learner’s Needs, and the father of two elementary-school math learners. He uses Bobby’s Math Club with his own kids a few times every week. Learn more or contact Bobby.
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Join the clubNote for teachers: This skill is covered by Common Core math standard K.G.B.4: “Analyze and compare two- and three-dimensional shapes, in different sizes and orientations, using informal language to describe their similarities, differences, parts (e.g., number of sides and vertices/"corners") and other attributes (e.g., having sides of equal length).” Learn how Bobby's Math Club can help your students grow. (Common Core K.G.4)