Hold up the piece of string (about a metre long) as you pose the question. Take three hands-up answers, not open call-outs. Give five seconds of quiet think-time first.

Write 1 m = 100 cm and 1 cm = 10 mm on the board as the anchors for the whole lesson. Listen for the idea that the string is the same length either way — revoice that as renaming.

1 cm = 10 mm: smaller unit, bigger number. Point at the digits.

3 cm to mm: multiply by ten, gives 30 mm. Keep returning to 1 cm = 10 mm.

2 m to cm: multiply by one hundred (1 m = 100 cm), gives 200 cm. Name it as a bigger jump.

150 cm to m: pause first, ask how many whole metres fit inside 150 cm? The converter shows 1.5 m, then name that yourself as the mixed length 1 m 50 cm.

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

Reveal each renaming in turn. Send one pupil up to set the converter, and have them say smaller — multiply or bigger — divide before they slide it. Rotate pupils across cm↔mm and m↔cm.

Watch for the common slip of dividing when they should multiply (or the reverse) — head it off by asking will the number get bigger or smaller? first.

These are the practice questions — 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.

For each one, prompt multiply or divide? before the pupil sets it. The final 325 cm needs them to enter 3.25 on the interactive (divide by 100). After it checks, call out that this is the same as the mixed length 3 m 25 cm.

Keep this brisk. Point back at the two anchors on the board one last time so pupils leave with 1 m = 100 cm and 1 cm = 10 mm firmly in mind.