Kids should be taught the basics of

*measurement*, not taught measurement systems. They can be introduced to them, so that they are aware of the different systems, but no one really knows these kinds of things until they are old enough to need them. Neither a kilometer nor a mile means much in the context of the average 8 year old.But an inch and a centimeter sure do mean a lot. I remember sitting there in school and realizing that I could easily guess how long things were in inches, after using them for so many years. Conversely I learned to weigh things in grams and it's very easy to estimate values when weighing.

I understand you are saying we should have the right to learn whatever system we want, or no system at all. I just don't see how it's possible to teach someone, say, language without them using grammar. Why do you feel so strongly about not teaching a particular measuring system? Are you against people teaching the standard clock, or should people decide how long they want their second to be? I agree that people shouldn't be pushed to accept what everyone else takes for granted, but at the same time we can't communicate without common language.

I teach my kids the units of measurements that they need for the problem at hand. My son's tape measure has both a metric and a AS edge. He could have chosen either, he chose to use the one that made the most sense to him at the time and in the context, which was a foot. He didn't use either inches nor meters, as either unit would have been less intuitive for his problem.

To illustrate this concept, take another practicum problem that I have not yet used on my kids. How do you weight a car, using only a pressure gauge, a pencil, a ruler and four sheets of blank paper? The answer is that you have Dad park the car over top of the paper, trace the footprint of the tyres, and measure the tire pressures. Then you use the ruler to make an estimate as to the area of the paper, multiply that by the pressure measurements, and add up all four results.

In AS, the pressure is Pounds-Per-Square-Inch so the paper traces are calculated in inches, and then the raw pressure measurement is multiplied. Add them up and you are done

However, in Metric the pressure unit is the Pascal, or the Newtwon/Meter. (No, I didn't remember that, like my own kids would do if they needed to, I simply looked it up) So to start with one would have to measure the area in square centimeters and then convert to square meters. Not that hard, surely, but an extra step. Then one would have to multiply out and add up, and end up with Newtons, a unit of

*force*instead of weight. If the unit is wrong, the answer is wrong; so we are looking for kilograms. To get there, we would have to involve the exceleration of gravity (2.2 m/s squared, if I recall correctly). So the math just got

**way**more complicated, unless the problem solver knew the shortcut that a Newton was (roughly) equal to 102 grams at Earth gravity or knew to look it up. But why would an eight year old know that, or choose to go to the trouble? This just illustrates what I have said about Metric in other threads, it workds well for sciences beause it was invented by scientists for their own ends. AS appears more complicated, but is usually more practical in practice becauseit was evolved by people who freely (in most cases) choose to use those particular units. The student should be able to use whatever unit of measurement he favors.