What is a Line of Symmetry? — Help Your Child Understand Shapes at KS1 & KS2

Symmetry is an important part of the maths curriculum at Key Stage 1 and Key Stage 2, and symmetry appears all over nature — often in extraordinary, beautiful ways. But what makes a shape symmetrical, and what is a line of symmetry? This guide will answer these questions, enabling you to help your child.

You can read the full article here. The full version also includes practice questions for your child to attempt.

What is a Line of Symmetry?

A line of symmetry is a line that cuts a shape in half so that if you were to fold the shape along the line, the two halves would overlap each other exactly. Here are some lines of symmetry that can be found in nature:

Symmetry in shapes

Some shapes are not symmetrical at all, while others have many lines of symmetry. Regular shapes are always symmetrical — they have as many lines of symmetry as they have sides. Irregular shapes can have lines of symmetry, but the more irregular they are, the less likely they are to be symmetrical.

How to find a line of symmetry in symmetrical shapes

In Year 2, children will learn how to find vertical lines of symmetry. They will need know whether a vertical line shown to them is a line of symmetry, and whether a shape shown to them has any vertical lines of symmetry. They will also learn to draw vertical lines of symmetry. Below is an example of an exercise in which the task is to identify the lines that are lines of symmetry:

In Year 4, children will build on this knowledge and learn how to find all lines of symmetry for 2D shapes as well as how to complete a symmetrical figure when only part of the figure is shown.

How symmetrical shapes work

A shape is symmetrical if it has at least one line of symmetry. You can turn any shape into a symmetrical one by reflecting it in a mirror and placing the mirrored shape next to the existing shape — the diagram below shows how this works:

Symmetrical shapes and their lines of symmetry are a key part of the maths curriculum at Key Stage 1 and Key Stage 2. We hope this introduction has been helpful as you support your child.