Measuring with Informal Units
From comparing to counting
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.
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.
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.
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.
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.
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.