Area and Perimeter Practice

Overview

In this lesson (Lesson 20 of 20), students practise solving measurement problems involving the area and perimeter of irregular and composite shapes. They will use unit-appropriate measurements and communicate their reasoning clearly, building on prior work with rectangular and non-rectangular regions.

Learning intentions

Students will:

• calculate perimeters of irregular shapes by adding side lengths (with correct units)
• determine areas of composite shapes by composing or decomposing into simpler shapes
• estimate area using grids where exact methods are difficult
• explain and check their answers using units and sensible reasoning

Success criteria

• I can find the perimeter of an irregular shape by adding all outer side lengths.
• I can find the area of a composite shape by breaking it into rectangles and combining areas.
• I can state my final answers with appropriate square units for area and linear units for perimeter.
• I can check whether my answer makes sense (size, direction of change, and unit type).

Curriculum links

• Measurement — solve problems involving the area and perimeter of irregular and composite shapes using appropriate units.
• Measurement — determine the area of composite shapes by composing or decomposing shapes.
• Measurement — determine perimeter and area of irregular shapes using covering measurements such as grids to approximate more accurately.

Lesson structure (30 minutes)

1. 0–3 min · Quick recap (activating prior learning). Teacher writes “Perimeter = around the outside” and “Area = inside the region” on the board and asks, “What units go with each?” Students respond with verbal unit examples (e.g. cm, cm²) and identify which measure each word describes.

2. 3–10 min · Worked example (teacher model). Teacher shows a simple composite shape made from rectangles (e.g. an L-shape) with side lengths labelled. Teacher models:

• perimeter: identify only the outside edges, then add lengths
• area: split into two rectangles, calculate each area, then add Students copy a short structure into their books: “Perimeter = outside edges + …” and “Area = rectangle 1 + rectangle 2 = …” using correct units.

3. 10–18 min · Guided practice: irregular shape task. Teacher hands out (or displays) one irregular shape problem with a grid overlay available (for approximation) and some lengths labelled (for exact perimeter). Students:

• find the perimeter using labelled side lengths
• choose one method for area: exact (if split is obvious) or grid approximation Teacher circulates and checks: correct identification of outer edges, correct use of square units for area, and whether decomposition matches the region without gaps or overlaps.

4. 18–25 min · Independent practice: two-question set (increasing accuracy). Teacher gives a short set:

• Q1: perimeter of a composite “step” shape (all outer sides labelled)
• Q2: area of the same “step” shape (given as a composite of rectangles) Students solve independently, show working, and round only if using grid estimates. Teacher prompts students to include a one-sentence check: “Does the area seem larger/smaller than a reference rectangle of similar size?”

5. 25–30 min · Exit ticket and check for understanding. Teacher displays a final mini-shape (small composite region) and asks for:

• perimeter (add outer sides)
• area (split into rectangles or use grid counting) Students submit answers with units. Teacher quickly scans for unit errors (common misconception: mixing cm and cm²) and for perimeter mistakes (counting internal edges).

Resources

• Printed worksheet or slide with 2–3 area/perimeter problems (including one irregular/composite shape)
• Centimetre grid paper (or square-grid overlays) for approximating area
• Rulers and coloured pencils (optional for tracing outer boundary)
• Marker/pen for teacher modelling
• Student workbooks and exit ticket slips
• Timer visible to students

Assessment

• Formative during guided practice: teacher checks students’ perimeter boundaries (outer edges only) and their area method (decompose/compose or grid).
• Unit accuracy check: teacher looks specifically for square units on area answers and linear units on perimeter answers.
• Exit ticket: evaluate correct method and correct units for both perimeter and area.

Differentiation

• Support:
• Provide a “split lines” guide on one example (students trace the decomposition).
• Sentence starters: “To find perimeter, I add the lengths of the outside edges…”, “I split the shape into rectangles…”.
• Use a grid that matches the given measurements to reduce estimation error.
• Extension:
• Add a challenge: “Estimate the area to the nearest square unit, then calculate the exact area and compare.”
• Ask students to describe how changing one side length affects both perimeter and area.
• EAL/SEN considerations:
• Keep language consistent: “outside edges” for perimeter, “inside region” for area.
• Use colour-coding: highlight the outer boundary in one colour, the area region in another.
• Offer step-by-step checklist on the worksheet for students who benefit from structure.