ACARA v9 CONTENT DESCRIPTION “measure the length of shapes and objects using informal units, recognising that units need to be uniform and used end-to-end”
In the last unit, children answered which is longer by lining things up. This unit takes the next step: saying how long something is, with a number. The trick is that Year 1 does not need rulers yet. Any small object can measure — blocks, paperclips, crayons, even thongs — as long as two rules hold. The units must all be the same size, and they must be laid end to end, with no gaps and no overlaps. Those two rules are the entire engine of measurement, and every ruler ever made is just these rules printed onto a stick. Children who feel why the rules matter will meet centimetres next year as old friends.
Lay them end to end
One block at a time: touching the last one, never overlapping it.
How many blocks long is the bat? Lay the first one at the very end.
End to end, like a little train
Measuring is counting — but counting copies of one length, coupled like carriages of a train. Each block starts exactly where the last one stopped: touching, never riding over. When the object runs out partway through a unit, honest measurers do not squeeze or stretch; they say about seven and a bit. That small word about is real mathematics — it admits the unit did not fit perfectly, which is the first step towards wanting smaller, finer units.
The gap trap
Same ribbon, same blocks. Watch the count change when the rules break.
Place the blocks and keep count.
When the count lies
The same ribbon and the same blocks can produce three different numbers, and only one of them is true. Leave gaps and the spaces quietly cover length that never gets counted, so the number comes out too small. Overlap the blocks and the same stretch of ribbon is counted twice, so the number swells. Children should be the ones to discover this: let the count go wrong, then ask the room why.
Mixed-up units
A count only means something when every unit is the same size.
Count the units one by one.
Six of what, exactly?
A count is a promise: six means six of the same thing. Mix big blocks with small ones and the promise breaks — the towel is six somethings long, and nobody can say what a something is. Uniformity is not fussiness; it is what lets one child’s measurement mean anything to another child. The moment a class agrees to measure with identical units, their numbers can finally talk to each other.
Big units, small numbers
Measure one surfboard with three different units and compare the counts.
Try all three units on the same board.
Bigger units, smaller numbers
Here is the relationship that quietly runs through all of measurement: the bigger the unit, the fewer you need. One surfboard is 4 thongs, or 8 crayons, or 16 paperclips — the board never changes, only the size of the step you count it with. Children often expect a bigger number to mean a longer object; this inverse twist is genuinely surprising the first time, and worth letting them feel on their own before naming it.
Whose desk is longer?
Two counts, two different units — and a trap hiding between them.
Mia counted 8 of her small hands. Tom counted 7 of his big hands. Different hands, different counts.
Why everyone needs the same unit
Mia’s desk is 8 hands long; Tom’s is 7. If hands were all the same, Mia would win — but hands are not, and counts made with different units simply cannot be compared. Re-measure both desks with identical blocks and the truth flips: Tom’s desk is longer. This little drama is exactly why the world eventually agreed on standard units — the road that leads, next year, to the centimetre.
Quick self-check
1. To measure a book with paperclips fairly, the clips must be...
2. A table is 6 thongs long, or 12 crayons long. Which unit is longer?
3. Sam leaves gaps between his blocks. His count will be...
4. Mia’s desk is 8 of her small hands. Tom’s is 7 of his big hands. Whose desk is longer?
5. A bat is 7 blocks and a little more. The best thing to say is...