The note
How schools teach it now
Children count squares first, then use formulae: rectangle = length × width, triangle = ½ × base × height, parallelogram = base × height (the upright height, not the sloping side). Perimeter is the distance round the edge; area is the space inside, in square units (cm²).
5-minute kitchen-table activity
Measure a placemat or chopping board with a ruler. Your child works out the perimeter and the area. Then: can they draw a different rectangle with the same area but a longer perimeter?
Worked example
A triangle has a base of 10 cm and a perpendicular height of 7 cm. What is its area?
- Area of a triangle = ½ × base × height.
- 10 × 7 = 70.
- Half of 70 is 35.
Answer: 35 cm²
Common mistakes to watch for
- Mixing up area and perimeter.
- Forgetting to halve for a triangle.
- Using the sloping side instead of the upright (perpendicular) height.
Encouragement
- Try saying
- “Are we measuring the edge or the inside?”
- Rather than
- “You've done this loads, why is it wrong?”