Saturday, August 9, 2008

Ask Mr D: Ideas for Teaching the Metric System

This question was emailed to me by reader Laura, who had enjoyed my 50 Cheap Mini-Lessons for Teachers. I don't get nearly enough questions as it stands, so hopefully this can become a regular feature here on the website. I love to be challenged to come up with new ideas!
Question: Do you have to teach the metric system? I've been told that it used to part of 6/7 math in my district but it has been cut - so now the kids don't get it until my class (8th science). I am not necessarily going for "understanding" early in the year - I hope that as they use it over the year they'll get more comfortable with it before "the test" in May. However, I'm looking for some strategies - mnemonics, poems, hand tricks, anything - to just help them get by until it sinks in. Thanks.

Answer: I don't have to teach the metric system, but I don't think you'll have too much trouble. If you teach them what the most often used prefixes mean (milli, centi, deci, kilo) and that the system always goes by tens, no matter what type of measurement it is, they'll get it pretty quickly. You might want to do a small scale project like the Independent/Dependent Variables poster where they have to show those commonly used measurements. I would guess your state exam probably asks them to do conversions (which they usually get a chart for) and for appropriate units of measurements, for example:

If I wanted to measure a football field, what unit of measurement would be most appropriate?
  1. centimeter
  2. millimeter
  3. meter
  4. kilometer
So, you could have them do a poster where they would draw examples of real life things that measure roughly 1 cm, 1 mm, 1km, etc or just an example of an item you would use that to measure. It would be something rather simple that they would be able to remember.

Another other key to getting kids to memorize something like that is that every time a question comes up that mentions those units, that you ask them what they mean (i.e."This question is talking about decimeters, how many centimeters is that?" or "Is that bigger or smaller than a meter?" or "Let's convert this to mm, cm, m and km just so we can remember what it means"). When I taught US History, the Texas 8th grade test had five key dates that students absolutely had to memorize, because they had been mentioned without fail on every test since it was created. So when any one of the five came up, I had them quickly rattle off all five. We also had five bulletin boards around the room dedicated to each of the years (each of which was of course a jumping off point to many other people, events and issues of importance). They always did well on those questions.

The last key, especially in a science class, is to remind them of the real life importance of getting measurements right and converting correctly. For example, there was that early Mars mission that failed because the the lander was designed to use metric units but calculations for landing were done with standard units. Also, you can talk about the Hubble Telescope and how the tiniest of mismeasurements caused it not to work and millions of dollars (and additional space missions) to fix it.

Now having said all that, you have to think about why exactly the metric system was cut from those previous courses. The answer is probably "it's not tested," which of course shouldn't be a legitimate reason, but is to everyone feeling the pressure of standardized testing. You have a long list of standards to teach yourself, and you need to critically evaluate where the metric system falls in terms of importance. I'm not saying don't teach it, but you should consider how much time you will spend on this topic. Perhaps you can integrate it with another topic to save time. Make sure you also look at what kind of questions they'll be asked on standardized tests, and that your lessons at least cover that material. You also need to think about what they'll need to help them in future classes and in college and work that into your lessons wherever possible.
Response: Thanks for taking the time to respond to my question so thoroughly. I
was actually going to open the "unit" (2 days :) ) on the metric
system using the Mars Orbiter mishap. I was also thinking of doing
some silly activity where we create 2 measurement systems on different
"bases" (like one of the larger boy's finger span versus one of the
smaller girl's hand span) to reiterate the importance of both a
standard system as well as accuracy in measurement.
I told her that was a great idea, as I had heard many math teachers using similar lessons with great success. Thanks to Laura for letting me share this, and don't be afraid to ask questions!