Take three hands-up answers on what the flattened box would look like; do not reveal the word net yet, it lands in the next step. Project a cereal box image (or unfold a real one) as pupils settle.

Rotate each solid slowly and narrate the three counts each time, in the same order: faces, edges, vertices. Cube: 6, 12, 8. Cuboid: 6, 12, 8 (same counts, different face shapes, point that out).

Then break out of the screen and pick up the printed cube nets you prepared: hold up the cross arrangement, fold it slowly into a cube in front of the class, hold up a second valid arrangement (a T-shape or staircase), then a deliberately invalid arrangement (a 2×3 block of squares, the two end squares end up overlapping when folded). Say it plainly: some six-square arrangements fold, some don't, we'll test six of them later.

Close the step by drawing a 4 × 3 × 2 cuboid on the isometric grid on the IWB: front face first, then back face one set of dots up-and-right, then join the matching corners. Narrate the rule out loud: horizontal stays horizontal, vertical stays vertical, slanting goes along the dots. Say the word isometric twice while you draw, once before and once after, so pupils hear it land on first meeting.

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

Hand out a printed cuboid net to every desk before you start (cuboid net printable). One pupil drives the IWB rotation; the class folds along with them. Pace the rotation aloud yourself, count 'rotate … and … fold' so the slowest folder isn't stranded behind the on-screen turn. Watch the board: when the on-screen front face turns toward us, every paper net should have its front rectangle on top of the stack. Use the moment one pupil's net doesn't match to teach the lesson, slow down, rotate the on-screen solid back, fold and re-fold the paper.

Then ask three pupils to come up in turn and trace the same cuboid on the isometric grid on the IWB. Watch for the slanting-edge mistake, a slant drawn freehand instead of along the dots is the most common slip. Revoice the rule: the slant follows the dots, never freehand.

Pre-cut the six arrangements before the lesson so pupils can move straight to folding and recording, cutting eats the time budget if left to pupils. The sheet has six arrangements: four are valid cube nets (the cross, a T-shape, a staircase, an L-shape), one is missing a face (only five squares connected, the sixth floats off), and one is the classic 2×3 block of squares where two faces overlap when folded.

Walk the room, the most common slip is calling the 2×3 block valid because it looks regular. Keep the reason categories tight on the board, just two: missing face or overlap. If a pupil isn't sure which applies, ask them to point at the gap or the overlap on their folded paper before they write.

If a pupil finishes early, point at the question on the board: can you describe in one sentence what's special about the four arrangements that DO fold? (Each square has at least one neighbour that's not on the same straight line, they bend in two directions, not one.)