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.

Walk each example aloud, one at a time.

• cm to mm — say smaller unit, so we multiply by ten and point at the digits.
• m to cm — say even smaller jump, so we multiply by one hundred.
• 150 cm — pause and ask how many whole metres fit inside 150 cm? before revealing the mixed answer.

Keep returning to the board anchors (1 m = 100 cm, 1 cm = 10 mm) so pupils see where every multiply comes from.

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.

This round is the practice bank — 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 see 300 cm = 3 m, leaving 25 cm — call that out as a 'split the leftover' moment.

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.