You’re teaching Year 5 next year and you look at what you’ve got to do in design and technology: “Moving toys using a cam.” You feel that headache coming on.

All modern technology is based on that of previous generations. The problem with all the modern examples is that the working bits are always cased in plastic so you can’t see how they work. If you are teaching children to make moving toys with cams, for example, this can create difficulties. The Qualifications and Curriculum Authority suggests making a collection of such toys for children to investigate. Easier said than done. In most modern toys the cam is very small or hidden inside.

I have been working with teachers to find a different starting point. The key feature of a cam is that it changes the direction of movement. So let’s do some history.

It is the start of the Industrial Revolution and Abraham Darby needs a very hot furnace to make iron. I ask the children what can help a barbecue to burn better. “Pour petrol on it” is a common suggestion. Eventually we get to blowing on it or fanning it. I show them an old pair of bellows and am met with: “My Gran’s got one of them.”

I explain that Abraham Darby needed bellows as big as a room and had only a waterwheel to provide the power. Waterwheels go round and round but the handles on the bellows go up and down. What could he do?

Instead of the conventional wooden frame joined with card triangles, the children all make identical structures with card and wood, punching holes through both pieces of card at the same time so the holes line up. This practical task allows the teacher plenty of opportunity to teach the correct techniques for cutting and joining.

Instead of drilling an off-centre hole in a wooden wheel to make the cam, I show the children how to punch a hole in a card disc and keep it in place with short lengths of plastic tubing. In a short time they all have a working machine, turned by a cranked handle rather than a waterwheel.

So far we have merely recreated history. How can we build on this? I ask the children what would happen if the cam were a different shape. We look at some possibilities and discover that we can have one movement of the cam follower for each turn of the handle, or two movements, or a slow rise and sudden drop. We also discover that the snail cam will only work if it is turned in a particular direction. Since we are using card to make the cams, there is no limit to the possible shapes that can be made.

How can we use all these ideas in the 21st century? Well, the pupils have all been to theme parks or shopping malls at Christmas and seen mechanical characters or creatures that move. They can choose the most appropriate cam for the effect they want to create.

You often read dire warnings of the effect you will have on children’s imagination by showing them completed examples. My experience has been very different. Given a blank canvas, one child will make a suggestion and all the rest will follow suit. I show children three finished models: a dinosaur that raises and lowers its head; a dog that wags its tail furiously; a long-necked bird that pecks its food.

Even the least able children improve on my models. The abler ones say my ideas are good but they can do better. The examples I show the pupils also provide a reference point they can return to if they meet with problems or need guidance.

The tools and materials used? Square-section wood, card, dowel, short pieces of plastic tubing, hole-punch, hacksaw, G-cramp, Wilson block and good quality PVA glue. As a safety measure, I always cut the dowel into shorter lengths before using it in class. Cereal box card is fine but remind the children to use glue on the matt, not the shiny side. Last of all, keeping the models small means they are stronger, quicker to make and easier to store.

The project has moved from the highly prescribed initial structure through the wider choice of cam to the free choice of the final model. It can be extended in a variety of ways: the models can be motorised and controlled by a computer. The children can put lots of snail cams together and explore how a ratchet works (especially useful if they’ve already done the “Winding up” project at key stage 1).

Have they actually made a “Moving Toy” as suggested in the QCA scheme of work? Probably not, but does that really matter? They have explored how cams have been useful in the past and are still being used today. They have also had fun - and so have I.

Diagrams courtesy of TTS www.tts-group.co.uk

Graham Samuel is a former primary headteacher. His book, Making Moving Toys with Cams is published by TTS, pound;10.95