How do you know just what problems will arise when you start making your product? Will you need any special jigs to hold the pieces in the right place whilst drilling, brazing, cutting or scoring takes place. Several of the projects you will have done at KS3 will have involved making a cardboard model to check out exactly what might go wrong - and GCSE projects are no different in that respect.
A simple item like this pencil holder might be improved by making a card model first. The addition of a thin bar joined to the base ( at the back right of this picture) would have prevented pencils from tilting at too great an angle
Alternatively by making the holder taller the pens and pencils can no longer twist in the way they did. An additional idea has been included in this model by adding magnets under the base so that paperclips can be held together without the need for any raised edges.
So now can you test your product before you have even completely made it !
Before making simple clocks like this one you will have been asked to make a card version first. This will have allowed you to see what problems there were in such things as drilling the hole for the clock spindle. In this model here the hole is at the very end of the pointed moon and without a little careful planning and positioning the end of the moon would have been lost.
Another more obvious example of when a prototype might need to be made can be seen here - Richard Buckminster Fuller designed innovative housing in the 1920's and 30's - without the benefit of computers the only modelling of his ideas he could do was with wood and card. By producing models to scale, testing could be done too. This kind of advance planning will help you to meet deadlines more easily and will show that you anticipated and solved problems before they occurred. The section called 'Planning and making' attracts nearly 50% of the marks . Get those marks !