Math lesson plan · 3rd grade (Year 4 in England) · 45 minutes
Area of composite rectilinear shapes
Geometry
CCSS 3.MD.C.7.DEngland: Y5 MeasurementEngland: Y6 Measurement
Objective and success criteria
Students will: Area of composite 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: Area of rectangles
Leads to: Area of compound shapes with missing lengths; Area of shapes made from rectangles and triangles
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 (Area of rectangles). 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: Area of composite 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 5 cm by 3 cm rectangle from the corner of a 8 cm by 9 cm rectangle. What is the area of the L-shape, in cm²?
- Step 1: 8 × 9 = 72
- Step 2: 5 × 3 = 15
- Step 3: 72 − 15 = 57 cm²
- Answer: 57
- 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 8 cm by 6 cm rectangle from the corner of a 12 cm by 9 cm rectangle. What is the area of the L-shape, in cm²? → 60Prompt: Find the area of the big rectangle.
- A garden is made of two rectangles: 8 m × 4 m and 7 m × 6 m. What is the total area, in m²? → 74Prompt: Find the area of each rectangle.
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 garden is made of two rectangles: 6 yd × 3 yd and 2 yd × 4 yd. What is the total area, in yd²? → 26Prompt: Find the area of each rectangle.
- An L-shape is made by cutting a 6 m by 5 m rectangle from the corner of a 9 m by 10 m rectangle. What is the area of the L-shape, in m²? → 60Prompt: Find the area of the big rectangle.
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: Area of rectangles.
- 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; Area of shapes made from rectangles and triangles.
- 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