Sunday, August 10, 2014

Loved that Lesson! - Volume of Prisms

Thank goodness for the ability of scheduling posts, am I right? For those of you who have been keeping up with me over the summer, you know that we are building a house and we are actually scheduled to close on MONDAY! So, today we are spending time packing up everything at my parents house so that we are ready to go when we get those keys. This however is not the real purpose of my post...

I am linking up with Meg from The Teacher Studio to share a lesson that I loved! You know the lessons that I am talking about...the one that went better than you ever thought it could. The kids were engaged, asking great questions, helping each other out, not one student was texting under their desk, and IN WALKS THE PRINCIPAL to do an informal walkthrough.

The heavens literally opened up and sang, "Hallelujah!" Things couldn't have been going better. That is the lesson that I am going to share with you today.

Yes, it is a past post, but since it is the summer, I haven't had any kids to teach. I tried to teach my dog how to lay down, but that didn't work so well--so I cannot blog about that. So without further is time for:

Y'all, teaching middle school math can be hard some days! Don't get me wrong, I love my job, but there are some things that kids just have a plain old tough time understanding. One of those things is the difference between volume and surface area. They don't understand conceptually where the formulas come from, therefore can't figure out how to solve the problems. I don't want to be that teacher who just tells them to use the chart and plug in the values, I want them to understand WHY that formula makes sense.

I SO wish that students aren't told to find volume by multiplying length x width x height. It takes me a full day to explain the formula V = Bh is the real formula for prisms. The one that they learn in elementary school only works for rectangular prisms, so that is fine until they get to my class, but most students feel like their whole life was a lie when that is no longer on the formula chart! I feel like I have to start from scratch and tell them that volume is a stack of 2D objects. We need to find the area of the base first. If I had a nickel every time I corrected a student regarding "b" (which is just base) or "B" (which is AREA of the base), I could have retired this week.

Literally, I am emotionally exhausted from saying, "what does big B stand for?"

Students respond with, "BASE!"

Me: "No. You don't get to say base loudly because it is a capital letter."

Students: "Oh, right! AREA of the base!"

My lord. I hope they still remember next week when we have a test.

One thing I wanted to share that they were JUST NOT GETTING was why we multiply by 1/3 for volume of a pyramid (and cones for that matter). I had finally sold them on the formulas for prisms and cylinders and they totally understood it conceptually. YES! But, then we hit a wall with pyramids. They wanted to know why we multiply by 1/3. Or divide by 3. Yes, we had a conversation that those were the same thing. Minds were blown. It wasn't enough for me to tell them that it takes the volume of 3 pyramids to make a prism. I had to show them.

I started with one of these:

Then, we made 2 more and taped them together at their apexes.

And, folded them up!

This TOTALLY helped them to visualize what I was saying. I love being able to let them PROVE things. It's the best. Love being able to use my washi tape too. It's the little things, right?

Here are some foldables that I created to use this week as well and are now in my TPT store! Click the pictures to go to the listing. 


  1. Hey Danielle, I totally love this idea! The only thing I am wondering if where did you get the template (or did you make it) for the prism? Especially love the wash tape ;)

    Teaching High School Math

  2. I sure don't envy you teaching middle school math, but this lesson sure looks like fun!

  3. I have the same question as Jennifer. Could you send a link to the template you used for the prism?