It appears that Fawn and I did this lesson on the same day… again. We teach over 100 miles from each other, but we appear to have some type of ESP that only affects the snarky.



Twice in the last three months, I have told a room full of teachers and education professionals to “take a risk, jump in, just go for it”, and I’ve used today’s lesson as an example. The Barbie Bungee (two years ago) was just dropped on students with no prior discussion and only a little planning on my part, and it went fine.

What I didn’t mention was that I did this lesson at the end of the school year after testing, when students are most likely to be thankful for a day outside and a weird lesson. A day without a clear learning objective was fine then.

Not so, now.

Toward the end of a unit on graphing (using prescribed curriculum that left some holes), we took a couple days to do the Barbie Bungee. I overhauled the handout completely… except it’s still pink.

When I say completely, I mean brain is a bit fried from making sense of the prescribed curriculum, and I forgot what students care about or what is mathematically important.

First, show a video.

In the first three seconds, students (and teachers in my workshop) gasp. They are hooked. Then, as a class, we discuss. “What do you think those guys were talking about as they drove out to the missile silo?” Student comments followed:

Will the rope break?
Will the rope be long enough?
Will anybody find my body before it freezes solid in the Russian wilderness?

“Why not get a short rope?” I ask. “My wife doesn’t want my brain mushed out my ears, and I might just use a seat belt for this jump.”
“Yeah, but that’s boring,” says Frankie. “Like, you wouldn’t have any fun.”
“Ah, so I want a really long bungee, then.”
“No!” Angelica jumps in. “Cuz if it’s too long, then you’ll hit the ground and die.”

Boom. Constraints established. A bungee jump should be fun, yet safe.

Like “Bear-Caging”, which is all the rage in British Columbia

Students brought dolls, were grouped into twos and threes, and did trials at three heights to find the maximum jump that was still safe. This was a change from last year, when students did three trials at five heights (a luxury from 90-minute periods that 55-minute periods do not afford).

It pained me to delete my beautiful table from previous years (attachment here), and even as I did it, something about the new lab sheet felt … lacking.

It wasn’t until my math coach came to visit (and I felt a bit self-conscious) that I realized what was missing:

The Point.

It was a fun activity with no point (just as before), except that now, I had stuck it in the middle of a unit without crafting student tasks around a learning goal.

The pink lab sheet and fun activity was just another disjointed set of operations with no attachment to the larger world of mathematics, the very thing I seek to avoid.

I also try to avoid bears, but luckily, there’s a cage for that.

I feel compelled here to note that Barbie Bungee does not fit into the adopted curriculum, but something like it would be necessary (more on that later).

Math Coach burst into my class at lunch. “The big jump. That’s the point. They are gathering data to derive an equation to solve for the big height so Barbie doesn’t die. That’s your point.”

IMG_2748 (1)

Here’s the issue with that: with an error hovering around 15% (and no training on line of best fit), my students’ equations were all over the place. One group calculated they would need eight rubber bands to jump off the roof (when 58 inches required six), and the group next to them needed 100.

Well, crap. I scrapped Bungee from that day.

Monday morning, I weighed all the Barbies on a food scale. Taking one from each weight class outside, I recorded my own data points (more than three apiece), and dropped them into Desmos, which is fast-becoming my go-to device for concrete-izing when something is too abstract.


Click here for my Desmos graph.

Now–one doll at a time–I call on students and move the sliders.

“Marco, should the slope increase, decrease, or stay the same? Maria, should the y-intercept increase, decrease, or stay the same? Alex, should the slope…”

Students were silent, every period, as they saw firsthand in real-time what it means to “increase the slope of a line”.

Also, there was no “right answer”. You wanna move the y-intercept down? Fine. The next student might move it right back up.

Can you imagine doing this by hand? Blech.

Eventually, students agreed that the line of each weight class passed through the respective points (for the most part), and we dropped the slider values into an equation for the number of bungees needed (r) to jump a certain height (h).

I passed out my Barbies to each group, and each Barbie matched up with an equation from a Barbie in a similar weight class.

And--feminist that I am--I didn't use the term "weight class".

And–feminist that I am–I didn’t use the term “weight class”.

Micro-managey? Sure. But when you teach RSP 8th-graders, you can’t exactly have the free-flowing hippie class that Fawn does. I made the choice to limit minor errors, so I need only correct ones pertinent to this unit.

Meaning I kept the long bungees from each period instead of waiting for groups to untie and re-tie them each period, and I labeled the legs of my Barbies, so they wouldn’t forget what her name was.

Also, duct-tape dresses.

A few minutes of calculating, a few more of tying rubber bands, and we’re off to the races.

Click to see video.

We spent the most time discussing how to fit the line to the data and why.

I’m okay with that.

~Matt “Middleweight” Vaudrey