On screen is a mixed tray: some flat shape cards, some solid shapes, and some angle cards, all jumbled together.

If you had to sort every one of these into groups, what is the very first question you would ask about each one to help you decide?

Watch the sorts on the board. Each one starts with a single property question. As each card is placed, get ready to say what question decided its group.

First we sort the flat shapes by how many sides they have. Watch a six-sided shape go into its group.

Now the question changes. To tell solid shapes apart we stop counting sides and start counting faces, edges or vertices.

Watch one full sort of solids by number of faces. We count every face of a cube: 6 faces, so the cube goes in the 6-faces group. Next, every face of a square-based pyramid: 5 faces, so the pyramid goes in the 5-faces group. The same method works with edges or vertices when that is the better question.

One good property question leads straight to the name and the group.

We will place these in turn:

• a square corner from a book
• the point of a triangular flag
• the wide corner of an open book
• an angle on a road sign
• the straight edge of an open ruler

Before each card lands, say whether it fits the square-corner test or not.