Congruent and Similar Shapes Background Information for Teachers, Parents, and Caregivers

This page contains information to support educators and families in teaching K-3 students about congruent and similar shapes. Designed to complement the BrainPOP Jr. movie Congruent and Similar Shapes, you will find ideas for developing related understandings and ways to use other BrainPOP Jr. resources to scaffold and extend student learning.

Help children explore geometry and understand and identify relationships between different figures.  Cut out a small square and a larger square from a piece of paper. Hold them up and ask children to compare and contrast them. How are these two figures alike and different? Help children see how both figures have four sides. Lead them to understand that they are the same shape—they are both squares—but they are different sizes because the lengths of each corresponding side are not the same. Then cut out two congruent rectangles from a piece of paper. Explain that congruent figures have the same size and shape. These two figures are both rectangles, and their corresponding sides are the same lengths. Slide one rectangle on top of another to show how they are exactly the same shape and size. Explain that if you stack congruent figures on top of each other, they match. Repeat the activity with other shapes. You may want to introduce polygons such as octagons, hexagons, and pentagons.

Take two congruent shapes and then turn one of them. Are the figures still congruent? Guide children to understand that when the shape is slid, turned, or flipped, it is still congruent with the other shape. The transformed figure has not changed shape or size. It has only been moved in some way. You may want to explore the movie Slides, Turns, and Flips as extension or review.

Now show a small equilateral triangle and a larger equilateral triangle. Guide children to understand that they are not congruent—they are incongruent, which means they do not have the same size and shape. One triangle’s sides are longer than the other triangle’s sides. Explain that they have the same shape—both are triangles—but they are different sizes. These figures are similar. Show several pairs of similar shapes. Be sure to point out how the figures are the same shape and have the same number of sides. However, the lengths of the sides are different. You may want to measure the sides of the corresponding sides of the triangle to compare. Repeat the activity with other similar figures. Remind children how similar shapes are incongruent.

Encourage children to slide shapes on top of each other to see if they are similar, congruent, or neither. They may also want to trace figures to aid in comparing and contrasting. Help children  find a technique that works for them.