Look at these three triangles on the board. One is tall and thin, one is wide and flat, and one is very pointy. They look really different from each other.

Hands up: what is the same about all three of these shapes?

The shape inspector lights up one side at a time. Count the sides with me as each shape appears. What is the same about the last two shapes?

We will look at four shapes together. For each one, count its straight sides aloud with the class, then decide: triangle, quadrilateral, or neither? Don't judge by how it looks, count the sides.

Now we build shapes with straws at the visualiser. A few pupils take turns to come up and build each shape, while everyone else checks the build by counting the sides aloud. Show a thumbs up if you agree the shape is right.

• Build a triangle.
• Build a square.
• Build a different quadrilateral that is not a square.
• Try to build a triangle using four straws, and tell us why it cannot be done.

What we learned today

• Any shape with three straight sides is a triangle, no matter how it is turned or stretched.
• Any shape with four straight sides is a quadrilateral.
• The trick is always to count the straight sides before naming a shape.

Coming up

Next we look at shapes with even more sides — pentagons, hexagons and octagons — and learn how their names tell you how many sides they have.