Math lesson plan · 4th grade (Year 5 in England) · 45 minutes
Perimeter of L-shapes and other rectilinear shapes
Geometry
CCSS 4.MD.A.3England: Y5 Measurement
Objective and success criteria
Students will: Perimeter of L-shapes and other rectilinear shapes.
- 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: Find a missing side from the perimeter
Leads to: Area of compound shapes with missing lengths
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 (Find a missing side from the perimeter). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
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: Perimeter of L-shapes and other rectilinear shapes. 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: An L-shape is made by cutting a small rectangle, 5 cm by 6 cm, from one corner of a big rectangle, 14 cm by 9 cm. What is the perimeter of the L-shape?
- Step 1: Sides: 14, 3, 5, 6, 9, 9
- Step 2: 14 + 3 + 5 + 6 + 9 + 9 = 46
- Step 3: 46 cm
- Answer: 46
- 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.
- An L-shape is made by cutting a small rectangle, 9 cm by 2 cm, from one corner of a big rectangle, 13 cm by 6 cm. What is the perimeter of the L-shape? → 38Prompt: Find all six side lengths of the L-shape.
- An L-shaped room has a long bottom wall of 10 m and a top wall of 3 m. How long is the short step wall that joins them across? → 7Prompt: Opposite sides of the whole shape must match.
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.
- An L-shaped room has a long bottom wall of 11 m and a top wall of 4 m. How long is the short step wall that joins them across? → 7Prompt: Opposite sides of the whole shape must match.
- An L-shape is made by cutting a small rectangle, 4 cm by 2 cm, from one corner of a big rectangle, 12 cm by 5 cm. What is the perimeter of the L-shape? → 34Prompt: Find all six side lengths of the L-shape.
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: Find a missing side from the 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: Area of compound shapes with missing lengths.
- 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-4.
Free lesson plan from eurekami.com/lesson-plan-builder