Symmetry mirror

What the mirror does

A shape has line symmetry when one half is the mirror image of the other half, so it would match exactly if you folded it along the line. On this page, choose a pen color and tap or drag to color squares on the grid. The tool reflects every square in the mirror line straight away. Choose a vertical line, a horizontal line, or both lines, which reflects each square into all four quarters.

In Complete the picture, one half of a picture is already drawn and the mirror is switched off. The child colors the other half so it matches, using the same colors. Check my picture tells them how many squares still need changing without saying which ones, and a cheer appears when the picture is perfectly symmetrical. New picture deals another one.

Why drawing reflections helps

The key idea in reflection is distance: each point and its image are the same distance from the mirror line, on opposite sides. A grid makes that distance countable. When a child completes a picture by hand, they have to count squares out from the line for every colored square, which is the same reasoning used later to reflect shapes on a coordinate grid. Drawing in mirror mode first lets them see the rule working before they apply it themselves.

Common mix-ups

• Copying instead of reflecting. Sliding the half across gives a translation, not a reflection; the square nearest the line must stay nearest the line.
• Counting from the edge of the grid instead of from the mirror line. Always measure from the line.
• Thinking only vertical lines count. Shapes can have horizontal or slanted lines of symmetry, or several at once.
• Expecting every shape to have a line of symmetry. Many shapes, like most parallelograms, have none.

A 10-minute symmetry session

• In Mirror drawing, color a few squares on the left and ask the child to predict each reflection before it shows.
• Switch to a horizontal line and repeat. Ask what stays the same about the rule.
• Choose Complete the picture and let the child finish the butterfly, counting from the mirror line.
• Press Check my picture. If any squares are wrong, ask the child to find them by counting.
• Finish with Both lines and let the child design a pattern of their own.

Where it fits by grade

• Grades 1 to 3: talking about shapes and their halves builds the language for symmetry. In England, Year 2 identifies vertical lines of symmetry in 2-D shapes.
• Grade 4: recognize lines of symmetry, identify line-symmetric figures, and draw lines of symmetry (4.G.A.3). In England, Year 4 identifies lines of symmetry in different orientations and completes symmetric figures.
• Grade 5: this grid work prepares for reflecting shapes on the coordinate plane. In England, Year 5 describes the position of a shape after a reflection, and Year 6 reflects shapes in the axes.

Learning more

Geometry skills like symmetry and angles are on Eurekami's skill map, and Daily Practice brings them back when they start to fade. Lessons draw diagrams live from the numbers in each question, and teachers can print worksheets with answer keys.