Lines of Symmetry

Overview

This is lesson 6 of 15 in Shapes, Space and Reasoning for five Year 4–6 learners. Students investigate symmetry by folding, reflecting and using mirrors to test 2D shapes, letters and classroom designs.

Learning intentions

• WALT identify and create lines of symmetry.
• WALT use folding, reflection and mirrors to test symmetry.
• WALT explain how two sides of a shape match.
• WALT use mathematical language to describe symmetry.

Success criteria

• I can show a line of symmetry on a 2D shape.
• I can check whether both sides match by folding or reflecting.
• I can explain why a shape, letter or design is symmetrical or not.
• I can create a shape with a specified number of lines of symmetry.

Curriculum links

• Geometry: recognise, describe and create 2D shapes and their properties.
• Spatial reasoning: visualise, transform, reflect and describe shapes.
• Mathematical communication: explain thinking using diagrams and precise vocabulary.
• Key competencies: thinking; using language, symbols and texts; managing self; participating and contributing.

Lesson structure (60 minutes)

1. 0–7 minutes – Visual hook and prior knowledge

Open with the symmetry hook slides. Show a familiar classroom object or design split down the middle and ask: “Would the two halves match if we folded it?” Introduce the signed and spoken vocabulary symmetry, line of symmetry, match, reflect and fold. Establish that a line of symmetry divides a shape into two matching mirror halves.

Use clear visual instructions, face the learners when speaking or signing, and check understanding through thumbs up/down or learner demonstrations.

2. 7–15 minutes – Teacher modelling

Demonstrate folding a paper rectangle, square, circle and scalene triangle. Mark each successful fold with a dashed line and model an unsuccessful fold. Use a mirror along a possible line of symmetry, explaining that the reflected half should complete the whole shape.

Invite learners to show the line with a finger or pencil. Emphasise that a shape may have zero, one or several lines of symmetry.

3. 15–28 minutes – Shape investigation

Give each learner a small selection of 2D shape cards from the 2D shape property cards. Learners predict, fold or use a mirror to test each shape, then record the number of lines of symmetry on the symmetry investigation worksheet.

Pause for demonstrations from learners: one student shows a fold, while another explains whether the two sides match. Support precise language such as “This is a line of symmetry because…”

4. 28–40 minutes – Letters and classroom designs

Display the letter and design examples in the letter and design investigation slides. In pairs or as a group of five, learners test selected capital letters and simple classroom designs using mirrors or transparent plastic strips. They decide whether each has vertical, horizontal, multiple or no lines of symmetry.

Encourage learners to explain their evidence rather than relying on appearance. Remind them that some letters are symmetrical in one orientation but not another.

5. 40–53 minutes – Create and challenge

Learners complete the design task on the symmetry investigation worksheet. They fold paper or use a grid to create a shape with a stated number of lines of symmetry, then draw and mark the lines clearly.

Advanced learners design shapes with two, three or four lines of symmetry, or create a shape with no lines of symmetry and explain how they know. They may challenge a peer to identify the number of lines without folding.

6. 53–60 minutes – Share and assess

Open the reflection and plenary slides. Select two or three learner designs for visual demonstration. Each learner completes the sentence: “My shape is/is not symmetrical because…” and shows the line or lines of symmetry.

Finish with a quick individual check: draw one line of symmetry on a shape shown on the final slide, then hold up the answer or demonstrate it with a fold.

Resources

• the symmetry lesson slide deck
• the symmetry investigation worksheet
• the 2D shape property cards
• Small mirrors or mirror strips
• Plain paper and pre-cut half-shape templates
• Folding supports and visual step cards
• Pencils, coloured pencils and rulers
• Transparent plastic strips or tracing paper
• Visual vocabulary cards with signed-language prompts
• Large paper for learner demonstrations

Assessment

• Observe whether learners accurately predict, fold, reflect and mark lines of symmetry.
• Listen for explanations that refer to two matching mirror halves, not simply “it looks the same”.
• Collect the worksheet and check shape classifications, labelled lines and the created-shape task.
• Use the final demonstration to identify learners needing further support with reflection or the meaning of “match”.

Differentiation

• Provide half-shape templates, pre-drawn fold lines, folding supports and visual step cards for learners who need reduced drawing or reading demands.
• Allow learners to respond through folding, pointing, drawing, signing or demonstrating before writing an explanation.
• Use enlarged, high-contrast shapes and uncluttered visual instructions; keep hands and faces visible for Deaf learners and provide signed vocabulary where available.
• For learners ready for challenge, investigate shapes with multiple lines of symmetry, compare regular and irregular shapes, or design a shape with a specified number of lines and justify the result.