Show the carton and the 10 cm cube side by side (or the images) as pupils settle. Take three hands-up answers, not open call-outs. Hold the reveal for Watch and Notice.

Listen for pupils who say the carton "looks bigger" because it is taller. That hunch is exactly what this lesson unpicks.

First box, 10 cm cube: point to each 10 cm edge, ask the class what 10 × 10 × 10 comes to before naming 1,000 cm³ = 1 litre.

Second box, 20 × 10 × 5: different shape, same 1,000 cm³, same litre. Pause and let a pupil say why before confirming.

Converter: litre to ml is three × 10 steps = × 1,000, so 1 litre = 1,000 ml. It stops at ml.

Last rung is in their heads: 1 ml = 1 cm³, so this step is × 1 and the number doesn't change. That makes 1,000 ml = 1,000 cm³, so 1 litre = 1,000 cm³.

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

Set the converter to volume. The converter works in l/ml only, so before the cm³ job the class swaps 2,500 cm³ for 2,500 ml (they are the same size), then divides by 1,000 to reach 2.5 litres. For each value, ask "multiply or divide, and by what?" before a pupil drives the chain.

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 converter works in l/ml only, so swap the cm³ value for the same number of ml before feeding it in (they are the same size): 3,000 cm³ becomes 3,000 ml, which divides by 1,000 to give 3 litres.

The converter cannot do the multiplication for the fish tank, so work out its volume on the board first: 30 × 20 × 25 = 15,000 cm³. The challenge card is pre-loaded with 15,000 ml so pupils see where the number came from. Then divide by 1,000 to reach 15 litres. Let a pupil predict the litres before the divide.