Area and Perimeter
Squares inside, or fence around the edge?
For grown-ups
- How long: 10 to 15 minutes is plenty. Short and frequent beats long and occasional — the early-numeracy trials with the largest effects ran eight weeks or less.
- When they get one wrong: the page shows the working. Read it together rather than moving straight on. Feedback that explains is worth several times more than feedback that only marks right or wrong, and that gap is wider in maths than in any other subject.
- Not timed: thinking time is the point of a book. Let silences run.
- Print it too: doing the same problems on paper a few days later is worth more than doing twice as many today.
What this practises
Finding the area and the perimeter of a rectangle, and telling them apart.
Area on a grid is the same array model used for multiplication, which is why it belongs immediately after the times tables. Perimeter is interleaved deliberately: mixing the two is what forces a child to read the question instead of multiplying whatever they are given.
- The underlying idea
- Area is the array model measured; perimeter is a different quantity on the same figure.
- Where this sits in Illustrative Mathematics
- 3rd grade Unit 2: Area and Multiplication · 3rd grade Unit 7: Two-dimensional Shapes and Perimeter
- Sources
- Illustrative Mathematics / Kendall Hunt (2024) · youcubed et al. (2015) all references →
Related measured skill: ALPACA · Elementary operations. What this means