What Is A Line Of Symmetry: Symmetrical Shapes Explained For Primary School

Lines of symmetry are a challenging concept for many pupils. This guide helps explain what a line of symmetry is and provides a few practice questions to test pupils’ skills.

This blog is part of our series of blogs designed for schools and teachers to help primary school age at any point of their lines of symmetry learning journey.

What is a line of symmetry?

A line of symmetry is a line that cuts a shape exactly in half.  

In symmetrical shapes, like a regular polygon, this means that if you were to fold the shape along the line of symmetry, both halves would match exactly and be mirror images of each other. If you were to place a mirror along this line, the shape would remain unchanged.

However, if shapes and objects do not have two identical halves when divided with a line of symmetry, they are asymmetrical figures.

Lines of symmetry in different symmetrical shapes

Each shape has a different number of lines of symmetry, whether it’s a quadrilateral rhombus or parallelogram, a scalene triangle or isosceles triangle, children should understand that each shape has different lines of symmetry.

For example, a square has 4 lines of symmetry, as shown below.

An equilateral triangle has 3 lines of symmetry.

Pupils can practice identifying lines of symmetry using this free symmetry worksheet for Year 4.

Number Of Lines Of Symmetry

As well as having different numbers of lines that split the shape into identical parts, the lines can also be in different positions. For example, diagonal, horizontal or verticle.

Each symmetrical shape also has a different axis of symmetry. For example, a heptagon has 7 angles each with a diagonal line of symmetry. While a hexagon has 1 horizontal line of symmetry, 1 vertical line of symmetry, and 4 diagonal lines of symmetry.

So there are different types of lines of symmetry depending on the shape.

When do children learn about lines of symmetry in primary school?

Children are introduced to symmetry in Year 2, where they are taught to identify and describe the properties of 2-D shapes, including the number of sides and line symmetry in a vertical line. 

This is then developed in Year 4, where pupils will identify lines of symmetry in 2-D shapes presented in different orientations and complete a simple symmetric figure concerning a specific line of symmetry. 

The non-statutory guidance also recommends that children recognise line symmetry in a variety of diagrams, including where the line of symmetry does not dissect the original shape.

Line of symmetry examples and practice questions

To practice lines of reflection symmetry, you can draw an imaginary line or mirror line onto different shapes. Or you can use practice questions like:

1)  Here is a shape on a grid. Complete the design so that it is symmetrical about the mirror line. Use a ruler.

2) These two shapes are made from equilateral triangles. Draw one line of symmetry on each shape. Use a ruler.

3) Here is a grid with eight squares shaded in. Shade in two more squares to make a symmetrical pattern.

4) The letter D has a line of symmetry. Tick all the other letters that have a line of symmetry.