When I first started teaching 8th-grade pre-algebra a few years ago, I looked everywhere for a good hands-on way to introduce and explore dilations. Turns out this is harder to find than the many ideas I found for rotations and reflections. I posted about my favorite way to teach rigid transformations last week – you can find that here.
I noticed that our 7th-grade math curriculum had a fun way to teach scale factors – using rubber bands. I started testing this idea to see if it would work for dilations on a coordinate plane. Turns out it works great!
How It Works
Tie two rubber bands together by looping one through the other. This creates a rubber band stretcher that will dilate a figure by a factor of two. Students will hold one end of the stretcher down with their fingers and put their pencils through the other end. Stretch the rubber band so that the knot is directly over the outline of the figure you are going to dilate. Pull your pencil so that the knot ‘traces’ the pre-image. You’ll have a dilation with a scale factor of two.
A couple of things to know if you’re going to try this:
- This method isn’t exact. Rubber bands are a little unpredictable and sometimes can stretch a little more or less than you want them to. However, this works pretty well and gives students a good intro and sometimes memorable to refer back to.
- If you’re having trouble with papers sliding around, try using some masking tape to tape the papers to the desks.
- The elephant in the room – middle schoolers with rubber bands. I know. I had this same fear. Before we started, I threatened them with their lives. (jk. mostly.) No, actually, I printed a boring dilations worksheet and explained that if I saw any rubber bands being shot or snapped, the worksheet was theirs, and they could do it in the hall. No second chances; this was their warning. It worked for all but one student, so I’ll take that as a win. I also collected the rubber bands as I was walking around the room and saw students finishing, so there weren’t any temptations lying around.
Here’s what you need
You’ll need some rubber bands. At least two per student, with some extras just in case. You can reuse them for the next class. I recommend pre-assembling the rubber band stretcher. I used these 3-inch rubber bands from Amazon. You could probably use 3 1/2 inch or 2 1/2 inch, but I definitely wouldn’t use anything larger than 3 1/2″.
You can do this activity with just some scratch paper and have students experiment with the scale factor, so they have a visual for dilating a figure. If you want a more in-depth intro to dilations, you can find my full activity here. It also comes with some good extra practice problems for students to work on once they’re finished.
