MathGrade 4ages 9–10
⬜ The around
Right after learning that area multiplies, a child asked for perimeter will often multiply again out of habit — turning a 3 by 5 rectangle's perimeter into 15 instead of the 16 you get by adding all four sides.
Try this lesson freeNo card needed. The first lesson is free.
Download on the App StoreWhat your child learns
- Perimeter is how long the walk around the shape is.
- Add every side you walk along.
- In a rectangle you walk four sides, not two.
- Multiplying gives the cover inside, and that is area.
The mistake most kids make here
Multiplying as if it were area.
Try one question
A rectangle with sides 3 and 5. What is the perimeter?
The walk around
- 8
- 15
- 16
Answer
16 — Yes. 3 plus 5 plus 3 plus 5 is 16.
How Maya teaches it
Your child tells Maya what they did in class. She teaches this topic at her desk, asks questions with tappable answers, and when the answer is wrong she explains why that answer was tempting instead of saying “try again”. She remembers what did not land and comes back to it.
Your child has it when they can: A 3 by 5 rectangle — what is the perimeter?
How to help at home
Perimeter and area answer two different questions using the same two numbers, and mixing them up is one of the most common mistakes right after area is introduced. Perimeter is about the edge you'd walk along; area is about what's covered inside.
Use a real rectangle — a rug, a table, a garden bed marked with string. Walk your child around the outside, counting each side length out loud as you go: 3, 5, 3, 5 — then add those four numbers together to get the total walk.
When your child multiplies the two sides for perimeter, say: "let's actually walk around it and count each side" and physically trace all four edges together before adding them up.
A sign they've got it: they can say, without you asking, that perimeter needs all four sides added while area needs the two different sides multiplied — and explain why in terms of walking around versus covering inside.
Questions parents ask
- Why does my child multiply the sides for perimeter, the same as for area?
- Area and perimeter get taught close together and use the same two numbers, so it's easy to apply the wrong operation out of habit. Physically walking the edge and adding each side as you go breaks that habit.
- What age do kids learn perimeter?
- Perimeter is usually introduced around the same time as area, in grade 3 or 4, once a child is comfortable adding several numbers together.
- Is there a shortcut for perimeter of a rectangle?
- Once the idea of adding all four sides is solid, most children discover on their own that opposite sides match, so you can double one side, double the other, and add those two results — but that shortcut should come after the hands-on counting, not before.
- How does Maya teach perimeter?
- Maya asks the child to add each side of the shape one at a time rather than offering a formula, so the walk-around idea comes before any shortcut.
No card needed. The first lesson is free.
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