It is Sunday evening, and you just cannot find the one gadget that might help along tomorrow’s lesson. Summoning the spirits of Blue Peter presenters past and present, you knock something up from cardboard and cling-wrap that does the job, even if it looks sad and worn by the end of Monday. Could your idea live on and be useful to others?

Linda Mangles asked herself this question while working as a non-teaching assistant for children with emotional and behavioural difficulties at Thybergh comprehensive in Rotherham. She went on to patent, manufacture and sell her creation: the Flexitable folding multiplication table now on sale to schools for less than pound;1.

Linda came up with the idea of a folding multiplication table in 1993 to help her sons Daniel and Peter (then six and eight) to learn their tables. At the same time she was taking evening classes at Dearne Valley college for a BTEC in child development which required her to develop a classroom resource. She made a number square, roughly seven inches by seven inches, with the numbers 1 to 12 along each of the four sides and their products in the centre. Back home, she tried it out on the boys. “I used it as a game as I peeled the spuds at the sink. I would ask them, ‘What is four times three?’ and they would fold the square width-ways across from the 4 and length-ways from the 3. Basically, you find it and fold it, and the answer is in the right-hand corner.”

The head of maths at Thybergh comprehensive advised her to get it patented. “He said that he used resources like this on a daily basis, but he had never seen it done in such a simple but effective way.”

Her next stop was Rotherham Business Link, where she was told that she would not be able to patent or sell her invention but was encouraged to go on a business course, which she could not afford. so she looked up “patent lawyers” in Yellow Pages and found Atkinson Burrington in Sheffield under A. Although the firm did not usually handle small projects, it was interested. The lawyers saw so much potential in Linda Mangles’s creation that they offered to waive her development costs until it made a profit and to help towards the pound;5,000 cost of US and UK patent applications, which they started in 1997.

The designer who produced the firm’s technical drawings was also a mechanical engineer with expertise in plastics. He tured Linda’s version into something that could be mass-produced, in the process reducing the grid from 12x12 numbers to 10x10, adding colour (red for the numbers round the outside; blue for the answers in the middle), finding a hard-wearing, flexible and foldable plastic; rounding the corners; and making sure the inks stood up to safety requirements.

Just over a year after the application was made, the Flexitable was patented in the UK and the US in original and Braille versions. But can they be sold? Ralph Atkinson, one of the partners, approached a marketing specialist, Tony Campbell, who toured the Education Show with a suitcase full of dummies and set up a website for online sales. So far he has sold more than 28,000 Flexitables and has just taken a big order from a dyslexia support centre. He hopes Flexitable will soon be in a major supplier’s catalogue. “We still have some way to go,” says Mr Campbell. “Getting shelf space is difficult.Shops plan their product range six months in advance; if you miss the selection date you can be shut out for a further 12 months.”

With so many adults involved, it’s easy to forget that Linda’s original aim was to help children and teachers with maths. Year 2 pupils at Mitchell Brook primary in Neasden, north London, were among the first to try the Flexitable in numeracy hour. Their verdict? “You can bend it so you don’t get mixed up,” says Shauna Whitely. But Jodie Nelson isn’t sure it is completely fair:“It tells you the answer when you’re supposed to work it out for yourself.” Their teacher, Theresa Landreth, can see a future for the Flexitable. “We used them as part of mental maths and to check our work. It would also be useful for key stage 2 special needs pupils.”

Linda has now left the classroom, but she is delighted that her resource has got this far. For her, the high point of the past three years was “finally seeing the first dummy all that time after making that first nervous phone call and thinking about my first home-made effort. I am not the brain of Britain, but I have developed something that mathematicians have not thought of before and it’s such a simple idea.”

She would advise others to follow the patent path. “If you have got an idea, no matter how simple, and you know that a child will achieve something using it, then seek advice, ask around, phone people up, don’t sit on it.”

Well, I have this toilet roll, an egg box, a pipe cleaner and some Sellotape. I wonder

Flexitable costs pound;9.95 plus VAT for a pack of 10. More details on www.flexitable.com.