Look at the shapes on the board: a triangle, a square, a rectangle, a circle and a hexagon. If I asked you to put just the shapes with four corners into one group, which ones would you choose?

Hands up and tell me one shape that goes in, and one that stays out.

Four shapes are shown below. Look at each one in turn and count its sides and corners.

Now we sort together. I will name one sorting rule each time. A pupil comes to the board and taps a shape to reveal how many sides and corners it has. Everyone at your desks says yes or no out loud before we decide which group it belongs to.

Now sort your own cut-out paper shapes at your desk. I will give you one rule at a time, and each rule gets a little harder.

For the next rule, keep the shapes that have exactly four sides. Then keep the shapes that have four sides and all of them the same length. Finally, find the shape that has four corners and four equal sides, and explain why it is the only one left.

What we learned

• We can sort the same set of shapes in different ways by choosing one property to check.
• A sorting rule must stay the same for every shape we test.
• One shape, like a square, can belong to two groups at once.