Perimeters of polygons
Solve problems involving perimeters of polygons: find perimeter from side lengths, find an unknown side length, and explore rectangles with same perimeter but different areas (or vice versa)
Lesson
Set out your lesson
“Perimeters of polygons means practising the idea at the table with counters or paper models and one clear check. We will demo once, then your child tries.”
Bring to the table
- Paper shapes or a ruler and pencil
- Shape name cards
Extra for the adult
Worked example. A rectangle has four right angles. Naming the property is the check.
Optional challenge. For Perimeters of polygons, add one harder example after success.
What to notice. Keep one parent note: examples tried; results; support used. This session samples Perimeters of polygons, not mastery.
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Teaching approaches
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1 approach
Perimeters of polygons means practising the idea at the table with counters or paper models and one clear check. We will demo once, then your child tries.
Materials: Paper shapes or a ruler and pencil; Shape name cards. Adult traces or shows one shape and names a property (sides/angles). Child identifies three shapes or measures one simple property and records it. Done: three correct shape/property responses. Stop after the fresh check; keep optional challenge for another day.
Family records and proof options
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Practice this concept
Start practicePerimeters of polygons practice
Practice key ideas from Perimeters of polygons.
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Learning resources
Extra practice links — they do not replace Gakuva’s teaching approach.
Illustrative Mathematics · Practice link — not the full lesson
Rectangle Perimeter 2
Before you open · source notes
Rectangle Perimeter 2 supports perimeters of polygons with equivalent expressions. Not every area model.
Free, no sign-in. A teacher solution is on the same page, so use the student view with your child.
Before you openAsk the learner to write two equivalent perimeter expressions for a rectangle.
Opening this link does not save learning or assess mastery.
Source, access and review notes
Public Illustrative Mathematics task page. The .html address responds HTTP 308 to this URL. An anonymous GET of this URL on 2026-11-12 returned HTTP 200 with no login or payment prompt. Where a teacher solution is present, it is on the same page as the student task; this check did not find a separate locked student view. An adult can use the student view section and should not read a solution aloud. Advertising was not observed in the fetched HTML text; that is not a browser, device, or ad-free guarantee. This is a paper or discussion task, not an automatically marked interactive game. Opening the link does not save practice or assess mastery. Diagrams on the page use missing or filename-only alt text, so they are not an accessible image equivalent. Accessibility still depends on an adult describing the picture.
Illustrative Mathematics. “Rectangle Perimeter 2.” Licensed CC BY-NC-SA 4.0. External task; Gakuva does not copy, host, embed, or redistribute it.
CC BY-NC-SA 4.0 — link only
Check understanding
- Calculate the perimeter of a rectangle with sides 8 cm and 5 cm
- Find the missing side of a pentagon with perimeter 30 cm and four known sides
- Draw two rectangles both with perimeter 24 cm but different areas
“If a rectangle has a perimeter of 24 cm and one side is 8 cm, can your child work out the length of the other side — without drawing it?”
Curriculum record
- Type
- Procedural
- Subject
- Mathematics
- Domain
- Measurement
- Age range
- Ages 8–11
Standards