Math lesson plan · 7th grade (Year 8 in England) · 45 minutes
Link radius, diameter and circumference
Geometry
CCSS 7.G.B.4England: KS3 Geometry and measuresEngland: GCSE Foundation Geometry and measures
Objective and success criteria
Students will: Link radius, diameter and circumference.
- 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: Circumference of a circle
Leads to: Area and perimeter of semicircles and quarter circles; Solve real problems with circles
Materials: Rulers and protractors, Squared or dotted paper, Shape cut-outs, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Circumference of a circle). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- A circle has radius 14 ft. Give its circumference in terms of π: it is kπ ft. What is k? → 28Prompt: C = 2πr.
- A circle has radius 9 cm. Give its circumference in terms of π: it is kπ cm. What is k? → 18Prompt: C = 2πr.
- A circle has radius 8 cm. Give its circumference in terms of π: it is kπ cm. What is k? → 16Prompt: C = 2πr.
Hook · 5 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: Link radius, diameter and circumference. Read the success criteria together.
I do: model it · 10 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: A circle has circumference 12Ï€ cm. What is its diameter, in cm?
- Step 1: πd = 12π → d = 12
- Answer: 12
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 10 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 circle has circumference 54π cm. What is its diameter, in cm? → 54Prompt: C = πd = 2πr.
- A circular running track has circumference 23 m. Find its diameter in metres, to 1 decimal place. → 7.3Prompt: C = π × d, so d = C ÷ π.
You do: independent practice · 10 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 8 questions are on the student sheet below, with answers in the key.
Exit ticket · 5 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- A circular running track has circumference 183 m. Find its diameter in metres, to 1 decimal place. → 58.3Prompt: C = π × d, so d = C ÷ π.
- A circle has circumference 60π cm. What is its diameter, in cm? → 60Prompt: C = πd = 2πr.
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: Circumference of a circle.
- 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: Area and perimeter of semicircles and quarter circles; Solve real problems with circles.
- 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