Hold up a real stack of a few cubes and one loose cube if you have them. Take three hands-up estimates, not open call-outs.

Don't reveal the count yet — the point is the guess, and the idea that some cubes hide behind others.

First solid (3 in a row): point to each cube as the class counts 1, 2, 3 — volume is 3 cubes.

Second solid (2 × 2 × 2): hold out for the hidden layer — "four cubes on the bottom, four on top, so how many in all?" Let the class predict the total before you confirm it is 8. The bottom-layer cubes are the make-or-break here.

Talk this one through together — pupils take turns at the board and the class agrees or corrects out loud.

Start by moving one stepper at a time yourself and reading the live count, so pupils see how a stepper maps to the total before they build. Then call a cube count, an individual pupil sets the steppers, and the class reads the live count to check it matches.

Before the count settles on a two-layer solid, ask a quick prediction: "how many do you think, counting the hidden layer?" and take two hands. On the hidden-layer check, turn-and-name a pupil: "did you count the bottom layer too?" Rotate three pupils across the three builds. Keep it brisk — the point is reading the count off the cubes, not perfecting the shape.

This is the practice round — pupils take turns at the board, check each answer, and the class confirms before moving on. Keep the board work brisk rather than over-explaining.

The 12-cube box steps us up gently from 8 before the 18. On the 18-cube box, read it layer by layer: "count one layer of 9, then the second layer of 9 on top of it — how many altogether?" Ask pupils for the dimensions they chose before checking, so they own the reasoning.

The 6-cube target is the one where the class sees there is more than one right answer: a flat row of 6, an L, a 3 × 2 slab all reach 6.