Mr. Stadel’s File Cabinet 3-Act Lesson

Monday evening I got a tweet from @mr_stadel:


Then he shared his uploaded File Cabinet – Act 1. I tweeted back, “Oh, I’ll start with this tomorrow then!! Thanks!!” Andrew had no idea I could really use a good lesson the next day to kick off our chapter on Areas and Volumes of Solids — specifically, Prisms.

Act 1: We watched the video and asked the question, “What’s the first question that comes to mind?”


As expected, some asked about surface area:

What is the area of 1 sticky note?

How many sticky notes are on that one side?

What is the surface area of the filing cabinet?

Others asked about volume:

What is the volume of the filing cabinet?

How many sticky notes will cover fill the file cabinet if the sticky notes were in cubes?

A few asked about time:

How long will it take to cover the whole cabinet with sticky notes?

And I got a WHY question from Bobby:

Why is he doing this so inefficiently? (Bobby said, “Since Mr. Stadel is finding the surface area, he should have just put sticky notes along the top row only, and then one layer downward, then multiply.” I asked, “Did Mr. Stadel say he wanted to find the surface area?” Bobby, “No… Okay, so Iwant to know the surface area.”)

Act 2: “What information do you need to answer your question?”

We did not proceed with the class asking one question. It seemed funny to ask them for an individual question only to make them answer someone’s else question instead. Therefore, I asked, “What information do you need to answer your question?”

I also decided to give them NO further information unless they specifically asked for it. They wrote down what information they needed:

  • an actual sticky note or a ruler, or the patent application for Post-it Notes™. (Yes, he wrote the little TM symbol.)
  • height and length of the cabinet
  • height and depth in sticky-notes
  • fraction of the sticky notes that took up the space
  • length of the sides of the sticky notes

I told them information was costly, and there was a limited budget. So if they asked me for two things, then they needed to rethink if they could do it with just one. Many decided they had the screen from Act 1 to try and get what they needed. They grabbed rulers and started measuring.



Bobby, above, wanted to measure the height for himself and told the class that the height was about 20 sticky notes. And that got Slater to say this:

After I stopped taping, Slater actually said add 3 to 4 to the height of 20 that Bobby gave. The actual height is 24 sticky-notes.

Many estimated the depth to be half of the width, and away they went — calculating surface area and volume.

I stopped short of showing the kids this Act 2 slide because I realized no one mentioned anything about the unit being in inches — they were content with the unit of “sticky-notes” that they saw in Act 1, and I didn’t want to disrupt this.


Act 3: The Payoff

@mr_stadel is finishing up Act 3; he emailed me part of it and I replied with, “You kill me, Andrew.” Later I saw @ddmeyer ‘s response to the same Act 3 image, “That’s a killer third act.”


The kids noticed immediately Mr. Stadel’s height and guessed between 6’3″ and 6’5″. He told us 6’4″.

After they figured out the surface area and volume in sticky-notes unit, I then asked if they could find the same in square inches and cubic inches. (I had the same 3″ x 3″ Post-it Notes in my room so they measured these.)

A: Why are you doing the problem again?

B: I need to change them into inches. Mrs. Nguyen said…

A: You can just multiply the area by 9 to get square inches.

B: Why 9?

C: Why not 3? Each sticky-note is 3 inches.

A: Each side is 3, so area is 9.

B: Oh, man, you mean I didn’t have to do the whole thing over?

Me: How do you change cubic sticky-notes to cubic inches?

A bunch of them: Multiply by… hmm… 27!

On their own, the kids also figured out the filing cabinet in square feet and cubic feet.

This was a great lesson, and I didn’t even do anything. Dan Meyer brought us his brilliant Three Acts. Andrew Stadel generously and enthusiastically shared with me this File Cabinet lesson. (I owe you at least a full cabinet of avocados!) Peter Price brought my name and blog into Twitter and showed me how to get started. I thank you all, and my kids thank you.

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