I came up with this geometry game awhile back after I had this conversation with a 4th grader:
- ME: What’s perimeter?
- 4th GRADER: It’s where when two sides are the same, then you um, I mean you times them by two.
- ME: Ok…I see where you’re going with that. But what does it mean, the perimeter of something?
- 4th GRADER: I know, but I can’t really explain it.
This girl had learned perimeter as just a random rule she needed to memorize. She didn’t understand that perimeter measures the outside edge of a shape; she just knew how to get the answer.
What she needed was an easy way to understand the idea of perimeter, so she’d be able to reason her way through a problem even if she forgets the rule.
Which is why I came up with the Perimeter Game–a super fun geometry game that makes sense of perimeter in a way kids totally understand.
HOW TO PLAY “THE PERIMETER GAME”
AGE: 7-11 years
PLAYERS: 2-4 players
BEST FOR: understanding what perimeter means
GOAL: Be the first to make a shape with a perimeter of 24 units
1. Roll the die. Take that number of tiles.
2. Use your tiles to make a shape. Each tile must touch another tile along a full side.
3. Count the outside edges of each tile in your shape. That number is your perimeter.
4. As your shape grows, you can choose to roll and take more tiles, OR to move one tile in your shape.
5. The first player to make a shape with a perimeter of 24 wins.
GETTING THE MOST FROM THIS GEOMETRY GAME
Here are some tweaks we made along the way that made our perimeter game even better:
- We kept playing after the first winner hit 24, to see who got 2nd, 3rd, and 4th place.
- I challenged the winner to find the area of her shape (counting total number of squares).
- I chatted with the winner(s) while the others played. We wondered if everyone’s shapes would have the same area. We talked about the difference between area and perimeter.
- The girls named their shapes. These girls made a robot and a torch, among other things.
COMMON MISTAKES TO WATCH OUT FOR
- The trickiest part of perimeter is understanding how to count the units. Some girls will want to count each whole side as one unit.
- Many kids count inside corners (“caves”) as one unit. Make sure they are counting each edge separately.
- It’s easy to lose count. We found that making a mark on the paper next to each square helped a lot. Some girls wrote the count for each side, then added them all up.
- A lot of kids forget where they started, so keep counting round and round, not sure where to stop. We started making a little mark at the starting place so they knew when they’d made it one time around.
QUESTIONS AND WONDERINGS ABOUT PERIMETER
I asked the girls some questions as we played…
- What did you notice as you played this game? What else did you notice?
- The robot and the torch both have a perimeter of 24, but the robot used 11 squares and the torch used 15. How can this be?
- How would you change your shape if you wanted a smaller perimeter?
- How would you change your shape if you wanted a larger perimeter?