Give five seconds of quiet think-time, then take three hands-up answers (not open call-outs). Don't push for the 'right' answer yet; the categories emerge in the next step. Listen for 'flat versus solid' (the 2D / 3D split); that's the lesson's main divide.

2D shapes (two passes through the same row)

Name the shapes first, asking the class to read them with you: triangle, square, rhombus, trapezium, hexagon. For the two that may be new to weaker readers: rhombus is a tilted square with four equal sides; trapezium has one pair of parallel sides. Flag that the triangle on screen is equilateral (all sides equal).

First pass — count the sides. Walk left to right and say the count for each: triangle 3, square 4, rhombus 4, trapezium 4, hexagon 6.

Show what a line of symmetry IS before counting them. On the IWB, fold the square (or use the mirror tool) down the middle so both halves match. Then across. Then on each diagonal. That's four visible matching folds. Now pupils have a concrete anchor for the count.

Second pass — count the lines of symmetry. Walk left to right through the same row: triangle 3, square 4, rhombus 2, trapezium 1, hexagon 6. Two narrations over one picture so pupils see the same shapes through two different sorting lenses.

Consolidation recap: ask the class to read the two passes back to you in order before we move to the solids. Hold the cube briefly on screen while the class catches its breath.

3D shapes

For each solid, rotate slowly while the class counts the three totals aloud with you.

• Cube: 6 faces, 12 edges, 8 vertices. The flat-face anchor.
• Triangular prism: 5 faces, 9 edges, 6 vertices. Two triangle ends and three rectangle sides.
• Cylinder: 3 surfaces, 2 edges, 0 vertices. The rule-bender. Say 'surfaces', not 'faces', because one is curved; and there are no corner points at all.

Do not rush the cylinder beat: it is the moment pupils realise the usual rules can flex.

This round is for talking it through together — pupils take turns at the board and the class agrees or corrects out loud.

Pick a shape on the inspector and ask the class to predict a property before a pupil reveals it: 'how many sides? how many corners? how many lines of symmetry?' A pupil at the board taps the matching button to show it on the shape, and the class checks its prediction. Work through the five shapes in turn — triangle, square, rhombus, trapezium, hexagon. Draw out two ideas: sides and corners always match on a closed shape; and lines of symmetry vary even when the side count does not (square 4, rhombus 2, trapezium 1). Flag that the triangle on screen is equilateral, so it has 3 lines of symmetry.

This round is for talking it through together — pupils take turns at the board and the class agrees or corrects out loud.

The shape-inspector-3d starts on the cube. Between rounds, the pupil at the board uses the shape selector to switch to triangular prism, then to cylinder. Confirm out loud each time — 'we're switching to the prism now', then 'and now to the cylinder' — so the whole class sees the transition rather than wondering what changed.

For each shape, the pupil drags to rotate the solid and taps each face, edge or vertex to mark it counted. The class counts each running total aloud. For the cylinder, hold the rotation and ask the class to point out the curved tube: it counts as one surface and bends the usual rule.

If polydron or real 3D solids are available, pass them around the desks so pupils can hold a real cube or prism alongside the on-screen one. The interactive is the canonical version; the polydron only verifies.