Nowadays there are many hands-on resources for practicing sorting, patterning and size. Sometimes even producers call plastic blocks 2D shapes, which is quite confusing and can lead to the further mathematical misconceptions for young children.
While the resources are very useful, because they can attract children’s attention to different attributes of the shapes, it is also very important to teach children the correct names of 2D and 3D shapes. It could be very misleading to call a triangular prism a triangle, or a cylinder – a circle.
As you may see in the National Curriculum in England (Updated 16 July 2014), in Year 1 (5-6 year-olds) children are already studying Geometry – properties of shapes. “Pupils should be taught to: recognise and name common 2-D and 3-D shapes”.
Of cause, you can always say, “For the purposes of this exercise, let’s think of these 3D shapes as 2D shapes” or “Today, we are going to call them triangles, but tomorrow they will be triangular prisms, as usually“, but isn’t it confusing?
Using Magformers for teaching 2D shapes can be even more confusing, because they are 3D objects and to describe their shape, you’d probably use the word frame. You’d say something like: “an object with triangular frame face”, which I can’t guarantee is correct. So, probably, not the best resource to begin with.
I think it would be more honest to call those objects with their proper names, whatever the learning objective of the lesson is. As long as you can pick up an object with your hand it is a 3D object.
So, how can we teach 2D shapes with these 3D resources?
It is correct to call them “shapes with 2D faces“. Thus you can avoid pronouncing new 3D names and concentrate on 2D names. Rather then arranging triangles, we can say
“Let’s arrange the shapes with triangular faces“.
“How many shapes with rectangular faces are blue?”
What is a 2D shape? No matter how thin the plastic object is, it is still 3D, because you can hold it. And even if you draw a rectangle on a piece of paper cut it and hold it up, it will still be 3D, because you are holding it up. You can even build a house with this object! (That’s what children are constantly demonstrating us! The whole nature is protesting – it is 3D – a 3-dimensional space, it means it has the height, the width and the depth.)
A 2D shape is not an object that you can hold, it is a picture.
To demonstrate the difference between 2D and 3D you can use a torch and make a shadow of an object (think of a cross-curricula link with Science topic Light). See how the shadow changes when you move the object.
Another way of demonstrating a difference between 2D and 3D is to put your block on a piece of paper and trace it with a pencil (or colour it and make a stamp). This is how you can get a hexagon out of a thin hexagonal prism. Moreover, this is how you can make a link to the good old concept of projection in mathematics to take your young inquisitive minds even further!
The good news is that you don’t need to waist your money on a special 2D set, take the 3D solid building blocks and enjoy your time exploring them, learning their names and of course sorting them out.