Before Common Core, teaching the Metric System to 5th grade students was not part of the 5th grade math curriculum in Kansas. So, last year was the first year I taught the metric system to my students. That experience turned out to not be a pleasant one. I think several things came into play: First, I, as a citizen of the United States have not been exposed to the metric system a lot. That unfamiliarity leads to an uncomfortableness when trying to teach. Second, students get bogged down with the Customary Measurement System (making conversions in particular) that they try to make the metric system more difficult than what it really is.
Fast forward a year and it is time to teach metric system conversions to my students. This time, however, I am ready. For one thing, I, myself, am much more comfortable with the content. In addition, what I didn't realize is that I had been laying the groundwork for the concept all year long.
Let me explain. With the new Common Core standards there is a real emphasis in looking for patterns and to embrace more than one strategy to solve an equation or problem. Manipulating numbers so that one can us mental math is also a big idea. All year long we had been practicing these very skills. When I realized I could apply what I'd been teaching all year to metric conversions, my life and my student's lives got a whole lot easier.
Back in September, we spent a great deal of time looking at multiplication and division patterns when working with multiples of ten. I even created 2 different sets of materials--Zero Can Be Your Hero - Multiplication Patterns with Multiples of 10 and Zero Can Be Your Hero - Division Patterns with Multiples of 10 for practicing the skill. After introducing early in the year, I then made a conscious effort to point out those types of problems anytime they showed up anywhere. After a month or two, all I would have to say is 'it's a Zero the Hero' problem and my kids knew exactly how to apply the pattern to solve the problem mentally.
And, then I had a 'light-bulb' moment...making metric conversions is like a big ole' Zero the Hero problem...well kind of...I had to call upon another source of groundwork that had been laid earlier in the year...'the invisible decimal'.
When we worked on multiplying and dividing decimals...I once again referred to Zero the Hero. I told them that you can apply the multiple of 10 pattern but instead of adding or subtracting zeros, you move the decimal. So, what happens if you divide or multiply by a multiple of 10 and the number being dividend or the factors don't have a decimal? That, my friends, is where the 'invisible decimal' comes into play. I told my students that every number has a decimal point. Some you can see (1.24) and some you can't see (124). When a number doesn't appear to have a decimal, you must locate the 'invisible decimal' (124.0) Again, I referred to the 'invisible decimal' any time it was appropriate.
So, here is what my metric conversion lesson using these two groundwork pieces and the top part of my Metric Measure Conversion Mat sounded like in my classroom yesterday...
Example Problem - 5000 kilometers = how many meters
First we looked at the metric measures mat. I had pointed out that the center box is our starting point, anything to the left of that starting point is larger and increases by 10 times (a multiple of 10 number) in size with each box. Moving right does the opposite. Then I reminded students what we learned when making customary conversions...to go from a large to a small, multiply. From a small to a large, divide.
I had them identify the measurements in the problem by placing a 'red marker' (small counter) on the kilometer box and a 'black marker' (small counter) on the meter box. Next, identify the fact that we are going from large to small so we will multiply. To determine what we will multiply by, I had them 'hop' the 'red marker' to the 'black marker' and count those hops as they go. There were 3 hops, so I asked them "What is the third power of 10?" 1000. So, I wrote the problem will be 5,000 x 1000, pointed out it was a "Zero the Hero" problem and they had 5,000,000 in no time.
Then I suggested another way...this uses both Zero the Hero and the Invisible Decimal...they liked this even better. Here's how it works...
Look at the number we are converting and find the 'invisible decimal'. Once you've found it, make it visible (5000.) Now look at your metric measures mat and find kilometers and meters. Which direction will you hop to make the conversion? (To the right.) How many hops? (3) Hop the invisible decimal 3 hops to the right and insert zeros to fill the gaps as you go (a skill we practiced earlier in the year). Stop after 3 hops. What number did you get? (5,000,000).
Easy as that! Now remember, my kids understand why this works because we have been doing this all year long. I would not recommend just showing this strategy without your students having an understanding of the pattern or concept.
I'm not going to lie, some students picked it up right and others took longer. As with any new math concept the key is to practice the skill over and over. But oh my, how much smoother it went this year as opposed to last. This summer I will be designing a bundle of products that will help you lay the groundwork and teach metric measure using this strategy. Frankly, I can't wait to get started :)