How do you teach children to measure? It starts with discussing differences in size or height. After a while it becomes clear that just talking about something being taller or shorter isn’t very precise, you need better language to discuss it. So you measure something.
One of the earliest lessons I when I was preparing to train as a teacher involved a class of six year olds measuring each other with plastic snakes. The snakes were different lengths, so it was far from reliable, but talking about someone being 4 snakes or 6 snakes long had more utility than simply saying one person was taller than another. When you know you are 4 snakes long you can find out if you are shorter or taller than someone. It’s not *that* reliable, but for the purposes of a 6 year old it pretty much works.
Later, as children’s discussions of height become more sophisticated they need more sophisticated tools, and to be taught standard measurements like cm and m. When I taught 8 year olds I had to do this lesson. They were all aware of these standard measures by this point, although exposure to their ubiquity had usually caused them to accept them without thinking too much about them.
The interesting discussions came when measuring things that were not a complete multiple of one centimeter in length. We could use fractions, but the understanding of those was often a little shaky. Usually the children decided we needed something smaller than a centimeter to do the job, and so I introduced them to millimeters.
One year some children got there before me, they subdivided their rulers into smaller units. They made up a new measure. It wasn’t millimeters, I forget whether they divided a centimeter into four, five or six, but what was important is that it allowed them to record and talk about the length of whatever it was they were measuring more precisely.
Who made up millimeters? I don’t know, although I’m sure a quick search would yield an interesting story, probably along the same lines as the one above. Unfortunately the children in my class had been beaten to it, and the standard has been set. However, the setting of it was probably not so different- someone made up a measure, people started using it and it stuck.
Standard measures are hugely useful. They let us communicate things precisely, manipulate them and explore them in the abstract. They are tools for representing a value with place on something- in the case of millimeters that it is valuable to be able to communicate the exact size of something.
The more we talk about measures, the more important I think it is to remember that they are all made up.
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