Math lesson plan · 7th grade (Year 8 in England) · 30 minutes
Scale factors and enlargement
Geometry
CCSS 7.G.A.1England: KS3 GeometryEngland: GCSE Foundation Geometry
Objective and success criteria
Students will: Scale factors and enlargement.
- I can answer questions on today's skill on my own, without help.
- I can explain each step and say why it works.
- I can check my answer and spot a mistake.
Before and after
Needs first: Scale drawings and maps
Leads to: Similar shapes; Dilations (enlargements) from the origin
Materials: Rulers and protractors, Squared or dotted paper, Shape cut-outs, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 4 min
- Quick retrieval from earlier learning (Scale drawings and maps). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- On a map, 1 cm represents 50 km. Two towns are 3 cm apart on the map. How far apart are they really, in km? → 150Prompt: Each centimetre on the map stands for the same real distance.
- A plan has scale 1:200. A wall is 28 m long in real life. How long is it on the plan, in cm? → 14Prompt: Change metres to centimetres first.
- On a map, 1 cm represents 2 km. Two towns are 12 cm apart on the map. How far apart are they really, in km? → 24Prompt: Each centimetre on the map stands for the same real distance.
Hook · 3 min
- Show a photo of a building, a tile pattern or a road sign and ask what shapes and angles students can spot.
- Share the objective: Scale factors and enlargement. Read the success criteria together.
I do: model it · 7 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: A 14 cm by 4 cm rectangle is enlarged by scale factor 0.5. What is the new length in cm?
- Step 1: 14 × 0.5 = 7 cm
- Answer: 7
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 6 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- A 18 cm by 16 cm rectangle is enlarged by scale factor 2. What is the new width in cm? → 32Prompt: Every length is multiplied by the scale factor.
- A side of 6 cm becomes 12 cm after an enlargement. What is the scale factor? → 2Prompt: Scale factor = new length ÷ old length.
You do: independent practice · 7 min
- Students work on the student sheet. Circulate and check the first two answers of every student early.
- Students who finish: write a question of their own for a partner, with the answer.
The 6 questions are on the student sheet below, with answers in the key.
Exit ticket · 3 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- A side of 4 cm becomes 8 cm after an enlargement. What is the scale factor? → 2Prompt: Scale factor = new length ÷ old length.
- A 18 cm by 4 cm rectangle is enlarged by scale factor 3. What is the new width in cm? → 12Prompt: Every length is multiplied by the scale factor.
Watch out for
- Thinking a square turned on its corner is no longer a square.
- Reading the wrong scale on a protractor.
Support and stretch
Support
- Review first: Scale drawings and maps.
- Use concrete materials: rulers and protractors.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Move on to: Similar shapes; Dilations (enlargements) from the origin.
- Explain a common mistake in writing and how to fix it.
- Write a word problem that uses today's skill, then solve a partner's.
Homework and more practice
Free online practice with hints and printable worksheets for this skill: eurekami.com/math/grade-7.
Free lesson plan from eurekami.com/lesson-plan-builder