When Things Go South

I’m teaching the basics of exponential growth to my fourth hour Algebra 2 class today. We’re using guided notes that I borrowed from another Algebra 2 teacher, which is new for this class; they usually take their own notes. Partway through I notice that everyone in the class looks extremely bored. Normally this class is talkative, and today they are quiet and looking anywhere except at me or their notes. I wonder if the guided notes have made things too easy for them. My goal was that they would be able to listen better if they didn’t have to spend so much time copying down notes. In the moment I notice their great disinterest, I start to panic inside. I hear myself talking and it sounds flat. All the energy is gone out of the room. How do I get it back???!? This is something that terrifies me in the classroom. It’s happened before and I haven’t figured out a fail proof way to handle it.  So I just keep talking. I feel like stopping and almost do for a moment, but what would I do then? After a minute, I remember that I had a video to show if there was time, so maybe I should just skip to that. As I’m getting ready to switch to it, I say to the class, I don’t know if you guys are bored or this is too easy or what. A couple of people mumbled that they were bored. Okay…. Was it me? Or their mood today? I don’t know.

So I go ahead and get the projector running and show a clip from Futurama about Fry checking his bank account. (See Dan Meyer's Three-Act called Fry's Bank).

Before Fry was transported in time he had 93¢ in his account. It had an interest rate of 2.25%. When Fry heard how much interest his 93¢ had accumulated over 1000 years (it was beeped out for the students so they could to figure it out), he started drooling and dropped on the floor. The students calculated the amount pretty quickly using a basic exponential function A(t) = a(1 + r)^t. (We haven't done compounded interest yet.) Then one student asked how much Fry would have in his bank account if he had started with $100 instead of 93¢, so we worked that out. We talked a little about how interest rates might change over time, the effects of inflation, and how much Bill Gates would have in 1000 years at a yearly interest rate of 2.25%. I enjoyed these slight tangents. After that we did another problem, and then I gave them 5 minutes to work on homework. I also gave them an exit slip and I was really surprised at the results – almost everyone felt it was easy!

I don’t know what the moral of the story is… Maybe to have something interesting prepared in case things go south? I was just glad we got through it and I was able to get the students’ attention back. A little confidence-booster for the future.