Building a Sierpinski tetrahedron at the Curious Minds Club (St Thomas of Canterbury Primary School, 14 February 2020)

I started this week’s session of the Curious Minds Club with some geometric snacks. First up were some nachos. I asked the children what type of triangle the nacho is. We talked about the Isosceles triangle last week, but none of them remembered. I wrote it on the whiteboard this week, to aid their learning.

Next up were some snacks I made, using cocktail sticks and midget gems:

Tetrahedron snacks

I told the children they could eat one if they could name the shape. One boy said triangle-based pyramid. I said this was correct, but that this shape has two names. I gave a hint about the first letter, and a girl very proudly said tetrahedron. I then handed one round to everybody, but made them all say tetrahedron first.

I explained that this week’s activity was to build Sierpinski’s tetrahedron, a three dimensional version of Sierpinski’s triangle. I showed them one part of it I had made using the generic version of Geomag that we used recently to build the Platonic Solids. I asked them to use just one colour to make the first part, then repeat this with a different colour. I got them to work in teams to add their four parts together to make a two layered Sierpinski tetrahedron. It involved removing some of the vertices, which the children worked out.

Two cousins (Y2 and Y4) made this (there was not enough dark blue to complete one part):


A boy and girl in Y6 made this:


For the rest of the session some children used the wooden pattern blocks to complete some more pattern boards. Others played Dotty Dinosaurs, a game about shapes. I asked two children to test a new game I have invented, with the working title of Plato’s Polyhedral Dice Game. Each child had five dice in the shape of the five Platonic Solids, and a dice cup. They had to race to complete tasks, such as roll five odd numbers. They seemed to enjoy it, although there was not enough time to get detailed feedback.

At the end of the session, because it was the last week of this half-term, I gave each child a gift to take home. I made these 2020 Rhombohedron calendars at home. I was testing different methods of attaching the parts of the net: PVA glue, glue dots, magnets. The winner was …. glue dots! The pdf is here.


I took all of the Sierpinski tetrahedrons the children had made home with me. I wanted to see if I could make one with three layers. I rearranged the parts, added two of my own, and came up with this, photographed from different angles:



Building some Platonic Solids to take home at the Curious Minds Club (St Thomas of Canterbury Primary School, 7 February 2020)

This week at the Curious Minds Club the children built models of the Platonic Solids to take home. In the previous two weeks I had given the children Polydron Frameworks and what I call a generic version of Geomag to make the Platonic Solids. These materials are expensive and I took them home at the end of the sessions. I wanted to give the children an opportunity to make models they could take home with them.

The materials I used were simple: plastic drinking straws and pipe cleaners. (I did ponder the ethics of plastic straws, as they are due to be banned in the UK in 2020; my conclusion was that I should use up the ones that currently exist before switching to paper). Feel free to contact me for details of the construction method. Once I showed the children how to build the models they took to it quickly. They enjoyed commenting on what the models looked like as they went along. When they were building a cube: “it looks like a laptop” and “I have made a table”.

Here are all five Platonic Solids that I made. (The session overran and there was no time to take photos of the children’s models). I think they look good in black. See how the pipe cleaners form the vertex:


Here is each one by itself:


They all look good …. until you get to the Dodecahedron above. This was a real struggle. My first attempt is below. The edge length is 75mm, the same as the others. It was hard to make every face look like a regular pentagon.


I thought I would try making each edge half the length (75mm to 37mm) to see if this was easier. This is how it looked during construction:

The end result is below. It was the best I could manage. I manipulated a lot of the vertices by switching the pipe cleaners around. It goes concave in places but the whole thing should be convex.


My conclusion is that drinking straws and pipe cleaners are a cheap and easy building material for building the Platonic Solids, if you can tolerate an imperfect Dodecahedron.

I also made a whole set using neon straws, but I don’t think they look as good as the black. You can see some gaps between the pipe cleaners inside the straws.


Starting to build the Platonic Solids at the Curious Minds Club (St Thomas of Canterbury Primary School, 24 January 2020)

This week at the Curious Minds Club we focused on three dimensional space by starting to build the Platonic Solids.

I gave the children some Polydron equilateral triangles and showed them the net of a tetrahedron. They were able to build one quite quickly, then form it into a three dimensional object. Next up was the cube. Before handing them the pieces I asked the children if they could work out the cube’s alternative name, based on it having six faces. With a little prompting to think about which two dimensional object has six sides, one girl correctly suggested ‘hexahedron’. The children then constructed their Polydron cubes. I did not show them all 11 nets of a cube (an activity for a later date?) but let them figure it out for themselves. The next was the octahedron. I gave each child eight equilateral triangles and told them that four triangles meet at each vertex. They found this a little harder and I showed them one I had made earlier as a guide.

I decided to leave the final two Platonic solids (the dodecahedron and icosahedron) to next week as I thought it would be too much to attempt all five in one session. I got out some magnetic rods and balls (similar to Geomag but a generic version) and asked the children to make the tetrahedron, cube and octahedron in this material. The Polydron pieces are good at bringing out each face of the solid, but the generic Geomag are better at bringing out the vertex and edge.

Some of the children built quite large cubes with three rods forming an edge. They soon discovered that this made a wobbly and unstable cube, due to the degrees of freedom in a square. I encouraged them to use one rod for an edge, and they had more success this way.

Below are some of the children’s creations:

Collection Platonic Solids1

Collection Platonic Solids2

I had prepared some material on the symmetry of the Platonic solids. I showed one girl how to look at each object in three ways: face on, edge on and vertex on. I gave her two dimensional pictures of each object and a piece of mirror card, and asked her to find the lines of reflective symmetry for each object. She did really well at this activity and seemed to really enjoy looking at the objects in different ways.

We finished with a quick game of Dotty Dinosaurs. This week we played the colour matching version as a memory game.

Regular and irregular pentagons at the Curious Minds Club (St Thomas of Canterbury Primary School, 17 January 2020)

This week at the Curious Minds Club we continued our exploration of shapes, in two and three dimensions of space, by looking at (regular) pentagons. The children were able to identify that pentagons do not fit together without leaving a gap or an overlap.

pentagon problem

I showed them how to cut two irregular pentagons out of a regular hexagon. They made a set and explored how to get them to tessellate with all the edges meeting at a vertex. The solution involved flipping some of the tiles over.

I gave one group the puzzle called Pentamania to explore. This is a set of 54 so called folded pentagons. Two can be seen in the image above (one pink, one grey) when regular pentagons overlap. The children solved one of the three puzzles and enjoyed making a pattern with the pieces.


Y6 girl PentaMania

A group of younger children enjoyed a quick game of Dotty Dinosaurs. They played the shape matching version.

dotty dinosaurs

We then made our first three dimensional object, a tetrahedron. I wanted to see how the children managed with the Polydron pieces I had, as they can be a little tricky for small hands to clip together. The children managed the activity well. One girl asked if she could take it home, so she must have liked it. I asked them what the object was called. One boy correctly said a triangle-based pyramid. They were all intrigued to learn its second name, the tetrahedron. I explained that tetra meant four in Ancient Greek, and this object has four faces.

. tetrahedron

We finished by getting out the pattern blocks from last week, and completing some of the pattern boards. Here are a selection: