Take two or three hands-up answers, not open call-outs. Give five seconds of quiet think-time first.

You are only fishing for the idea that we look at the marks either side and work out what is in between — don't confirm a number yet.

• 300 ml — first jug, steps of 100 ml, water sits on a mark. Ask what each step is worth before reading.
• 600 ml — second jug, steps of 200 ml; the step changed, so re-count before reading.
• 1 litre 200 ml — third jug, past the litre line; the numbers keep climbing past 1000 ml.
• 250 ml — the last jug; the water lands halfway between 200 and 300, so draw out that halfway means add half a step.

Say verbatim before each: what is one step worth here? The step size changes between jugs — that is the point to hold out for.

Send an individual pupil up to read each jug and check it; the class agrees or corrects out loud before you move to the next one.

Before each reading ask the class what is one step worth on this jug? Re-count the marks each time, because the step size keeps changing.

The 450 ml and 550 ml jugs use steps of 50 ml, so there is a mark right on each of those values — hold pupils to counting the smaller step rather than assuming 100 ml.

This is the practice round. Set up fixed stations, one jug and water tray per group of four, so each group works its own jug rather than passing one around the whole class. Pupils read the level after each pour and the group agrees on it.

Circulate and catch two slips on the spot: reading from above the water instead of at eye level, and reading the wrong step size when a jug's numbering differs. When a group reaches 1 litre, ask them to say it two ways — 1000 ml and 1 litre.