A young person may be able to read a measurement but still find it difficult to judge which real amount is larger, longer, heavier or more likely to fit. Comparing first and measuring afterwards links the number to the physical quantity.

Use a real decision

Choose a practical situation: which container will hold more, which box is heavier, which route is longer or whether an item will fit a space. Ask the young person to compare the options before using a scale, ruler, jug or map.

For example, when packing, ask which of two boxes is likely to hold more. Discuss height, width and depth, then check by measuring or filling them. The first impression may be misleading, which gives a useful reason to measure.

Describe the comparison

Encourage precise language:

• longer or shorter;

• heavier or lighter;

• greater or smaller capacity;

• approximately twice as much;

• close enough for the purpose.

The aim is not a perfect prediction. It is to connect visible features with the quantity being measured and to revise the judgement after evidence.

Keep the activity tied to something that needs doing anyway. If the young person repeatedly misjudges familiar units or cannot interpret the measuring tool, note the example and ask school which familiar measures or diagrams are being used in class.