A key objective in the Year 2 Measurement programme of study is to:
‘Compare and order lengths.’
Children should be able to order more than two lengths, from shortest to longest, at first using only the same unit of measurement. This will also help with ordering numbers to 100. Later, when confident with the knowledge that 10 mm = 1 cm and 100 cm = 1 metre they can begin to order measurements using mixed units.