Reflecting a Shape Across a Line

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1 Getting Started
2 Watch and Notice
3 Try It Together
4 Draw the Reflection in Your Copy
5 Class Challenge
6 What Did We Notice?
7 What's Next
Pupil practice

1 - Getting Started ~4 mins

Illustration for Getting Started Look at this picture of a pattern-block triangle standing beside a mirror. The triangle points to the right. Its reflection sits in the mirror.

Which way is the reflection pointing? The same way as the triangle, or the opposite way? Have a good look before any hands go up.

Teacher Notes

Give five seconds of quiet think-time, then take two or three hands-up answers. Listen for pupils noticing the reflection points the opposite way. Revoice: so the mirror flips it round to face the other side.

👇 Mark your steps as done as you complete them.

+5 XP

2 - Watch and Notice ~12 mins

The interactive reflects each shape across a mirror line. Watch which way the shape flips, and count the squares from the line to a corner and back the same distance on the other side.

Teacher Notes

Vertical line: triangle flips left to right, same size, never slid across.

Horizontal line: same triangle, flip is now top-to-bottom, same idea, different line.

L-shape: foot of the L swaps sides. Pick one corner, count 2 squares to the left of the line, so it lands 2 squares to the right. This equal-distance counting is the heart of the lesson.

Diagonal line: mark the slant clearly. Flip still keeps every corner the same distance, but count at right angles to the slant, not straight across. Builds the diagonal case before they meet it later.

👇 Mark your steps as done as you complete them.

+10 XP

3 - Try It Together ~8 mins

Today we explore reflections on the board. We build a small shape on one side of the mirror line, and the tool flips it across to the other side. Watch where each flipped corner lands.

Key point

We will try a triangle across a line, then an L-shape, checking each time that every corner is the same distance from the line.

Reflect the shape across the line

Teacher Notes

This round is for talking it through together — pupils take turns at the board and the class agrees or corrects out loud.

Invite an individual pupil to tap cells to build a small shape on one side of the chosen mirror line; the tool auto-mirrors each tap across the line. Before confirming each flip, do a quick turn-and-name: name a pupil to say how many squares one corner sits from the line, then name another to say where its reflection should land. Ask the class to check: is the flipped corner the same number of squares from the line? Rotate three or four pupils, revoicing a clear answer each time. Watch for pupils expecting the shape to slide rather than flip — pause and revoice when the reflection faces the opposite way.

+15 XP

4 - Draw the Reflection in Your Copy ~3 mins

COPYBOOK MOMENT

Illustration for Draw the Reflection in Your Copy In your maths copy on squared paper, draw a vertical mirror line. On the left of the line, draw a flag shape. Then carefully draw its reflection on the right.

Check each corner: count how many squares the corner is from the line, then count the same number on the other side. Every corner must be the same distance from the line.

Teacher Notes

Walk the room glancing at the corner counts and that the reflection faces the opposite way — this is whole-class copybook practice, not marking.

+10 XP

5 - Class Challenge ~10 mins

Key point

Today we work through these reflections together. Remember: a reflection flips the shape; it is never just slid along.

Reflect a triangle across a vertical line.
Reflect the triangle across a horizontal line.
Reflect an arrow so it points the opposite way.
Reflect a shape that touches the line.

Tip

If we have time, there is an optional stretch: reflect an L across a diagonal line.

Reflect each shape across the line

Teacher Notes

These are the practice questions — pupils take turns at the board, check each answer, and the class confirms before moving on. Keep the board work brisk rather than over-explaining.

Narrate the which way does it flip? question each time. The diagonal-line reflection at the end is an optional stretch — lead it explicitly with the class, marking the slant line and checking one corner's distance aloud together, and only run it if time allows. Watch for the slide-not-flip slip on the arrow shape: if the arrow still points the same way, it has been moved, not reflected.

+15 XP

Pupil practice

Module 8 · Symmetry, Location and Transformation Algebra

Lesson 93 · Reflecting a Shape Across a Line

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This lesson is copyright of Coding Ireland 2017 - 2025. Unauthorised use, copying or distribution is not allowed.

Teacher Class Feed

1 - Getting Started ~4 mins

2 - Watch and Notice ~12 mins

3 - Try It Together ~8 mins

Reflect the shape across the line

4 - Draw the Reflection in Your Copy ~3 mins

5 - Class Challenge ~10 mins

Reflect each shape across the line

Unlock the full learning experience

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