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. Your teacher will place a six-sided shape in 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. Your teacher will 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.

Today we work through four sorting rounds, each one a step harder:

• sort flat shapes by number of sides
• sort triangles into their three families
• sort angles into acute, right and obtuse
• a fully mixed set: choose the right question first

Before Round 2, we sort one triangle together on the board. We compare its three sides: if all 3 match it is equilateral, if only 2 match it is isosceles, if no sides match it is scalene. Then we place it in its family bucket.

Before Round 3, we test one angle together with the folded-paper square corner. If the angle is smaller than the square corner it is acute, if it fits exactly it is right, if it is wider it is obtuse. Then we place it in its bucket.

After each worked example, you take turns dragging the rest. Use Check when every card is in a bucket.