Geometry – Day 69 – Introduction to Solid Shapes

Come for:

  1. Classification of solid shapes.
  2. A nice self-contained classwork set + visuals.

Stay for:

  1. The start of our prep routine for state testing.
  2. The question: how does one teach Geometry without a digital projector? Do you have to draw these tricky solids by hand?


  1. None


Slide Deck

  1. Hole-in-one insurance. Sunday Times. Because if you nail a hole-in-one you are obliged to buy drinks, meals, and gifts for the entire clubhouse.
  2. This is not a pentahedron. This is a hexahedron. Number of sides.
  3. Talk about lateral faces. Lateral edges. Oblique.
  4. Ask them to sort things into pyramid & prism categories. This here’s a picture of an ingot.

Notes & Revisions:

I'm Dan and this is my blog. I'm a former high school math teacher and current head of teaching at Desmos. More here.


  1. I do a fairly cool activity with my middle schoolers, as we introduce polyhedrons (not as detailed as your students, but still dealing with prisms and pyramids/cones). It’d decidedly NOT technological, unless you consider a circle of paper to be high-tech. But with about a 7″ diameter circle of paper, you can fold it and discuss various polygons along the way, and wind up folding it to create a truncated tetrahedron. And then with a whole class of those (assuming that you have at least 20 students in the class), you can tape them all together and create an icosahedron. It’s pretty tactile activity, and it sure doesn’t lend itself to using a video projector, but for the most part my students always love it. And it makes a good model to keep pointing back at during subsequent lessons.

  2. Hey that sounds slick. I’m trying to imagine the progression. Do you know if the plans are available online?

  3. Yeah, here you go – it starts on page 26 of this
    PDF (actually, pages 26-30). Sorry, if I were at school with full Acrobat I could extract those specific pages for you. It even comes with a sample circle that you can print out (but I suspect that your Mac will allow you to draw circles too ;)

    Errata: I just realized that in my original post I said “polyhedrons” when I should have said “polyhedra.” My bad.

    Note: With this quasi-origami project, I’ve found that my ADD/ADHD students pay awesome attention, although it can turn into an obsession – one student apparently went home, proceeded to cut out and fold 20 circles for himself, and taped them into an icosahedron. He then hackeyed it around like a soccer ball until it fell apart, so he proceeded to make another 20 circles and fold them all again!

  4. Dang, this is great stuff. We just finished up testing, which means the heavy math lifting = over, so now seems like a great moment to appease my distractable kids who’ve been such troopers the last coupla days. Thanks, Rich.

  5. I’d say that the toughest part is cutting out the darned circle. While it’s not required that it be a perfectly smooth circle, it sure makes things work better. At our school, students are allowed to possess scissors, which made that task go much faster. If I’d had to cut them all out myself for all of my sections, I would have not been terribly happy.

  6. Hey, just checking back – did you try doing this paper folding activity yet, or are you saving it for later?

  7. We just got into Platonic Solids last week so that’s going to happen soon. I just need to coax someone to pimp out his t.a. for light scissor duties.