Math lesson plan · 3rd grade (Year 4 in England) · 45 minutes
Find a missing side from the perimeter
Geometry
CCSS 3.MD.D.8England: Y3 MeasurementEngland: Y4 Measurement
Objective and success criteria
Students will: Find a missing side from the perimeter.
- 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: Perimeter
Leads to: Perimeter of L-shapes and other rectilinear shapes; Area and perimeter in real-life problems
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 (Perimeter). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- A rectangle has a perimeter of 16 ft. Its length is 6 ft. What is its width, in ft? → 2Prompt: Two lengths plus two widths make the perimeter.
- A rectangle has a perimeter of 16 yd. Its length is 3 yd. What is its width, in yd? → 5Prompt: Two lengths plus two widths make the perimeter.
- A rectangle has a perimeter of 48 ft. Its length is 14 ft. What is its width, in ft? → 10Prompt: Two lengths plus two widths make the perimeter.
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: Find a missing side from the perimeter. 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.
- Model one question from the student sheet, thinking aloud.
- 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.
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.
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: Perimeter.
- 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: Perimeter of L-shapes and other rectilinear shapes; Area and perimeter in real-life problems.
- 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-3.
Free lesson plan from eurekami.com/lesson-plan-builder