The metric system is so important for students to understand in the sciences. And frankly, it's so much easier to use than the imperial system. One issue I've come across when teaching is that students don't always understand what the units represent, and which unit is appropriate to use for each situation (especially when measuring length). Here is an easy way for students to realize why we need different units of measurement.
I was at Ikea furniture shopping and realized that the disposable rulers they have for free all over the store would be an awesome teaching tool. I pulled the "teacher card" and asked if I could have a bunch for my classroom. The employee was happy to give me a class set of 40. (That was enough for me to group students in 4's across my 5 periods).
For this lesson, each group will need:
I started by giving each group one of the blank measuring tapes and asked them to measure the length of the lab table. Most groups came up with answers like "1 1/2 strips of paper", or "1 3/4 strips of paper" long. Next, I asked them to take the same blank measuring tape and measure the length of their school ID. It got harder for them to estimate the length since it was so much smaller. I got answers like "1/10 of the tape." We stopped and discussed that it would be better to have a smaller measuring tape to measure the length of the the ID. I asked them "Would you get a more accurate measurement if you cut the strip of paper in half?" They said that would still be too big. Quarters? Still too big. This went back and forth until we decided that cutting the strip of paper into 10 equal pieces would be just about right. I handed them scissors and asked them to cut it into 10 equal pieces and then measure the ID again.
The opposite scenario is also true: ask them how many strips of paper it would take to measure the distance between school and their house. Students will quickly realize that the measuring tape they have is much too small. Stop and have a conversation with your students about how it is important to have different units of measurement that are appropriate to the object being measured.
Finally, I switched out the blank strips of paper with the Ikea measuring tape. Have them make observations about the tape like:
Next ask them to take the Ikea measuring tape and cut it into 10 equal pieces. It should go much smoother this time now that there are numbers! Then ask them to take the 1/10th size paper (1decimeter, but they don't know this term yet) and ask them to cut it down again into 10 equal pieces (centimeters). Repeat this one more time until you have them cut individual millimeters. (See images below)
Have students discuss when it is appropriate to use each unit of measurement. I had them match objects to each length that are about the same size. For example, the meter strip is about the length of the floor to the door handle. The decimeter strip is about the length of the palm of your hand. The centimeter strip is about the width of your fingernail. The millimeter strip is about the thickness of their school ID card.
Following the activity we took notes on the metric system and units of measurement. I think students remember the units better when they understand that everything is based on powers of 10, and can relate the units to objects. One of my favorite phrases to use in the classroom is "NO NAKED NUMBERS!" It makes them giggle (especially middle schoolers!), but students know to not turn in papers for the rest of the year that have numbers with no units.
I hope this helps you teach the metric system! If you have any other tips and tricks, leave them in the comments! Also, you might want to check out these metric system posters and puzzles in my TpT store: