As schools return for the start of another academic year, teachers will be on the look-out for children with learning problems in their classes. Nick Foley discovers how they can tell if a child is dyslexic and asks what causes it.

IT WASN'T so long ago that dyslexics were treated as the classroom dunces by both their peers and their teachers.

Those affected were often bright and intelligent in conversation but hopeless when it came to reading and writing. They were a strange contradiction, but few ever questioned why this was.

Former world racing champion, Sir Jackie Stewart, 64, recently recalled in an interview how he was ''abused for being thick'' as an undiagnosed dyslexic at school.

Back then, if you had problems learning you were simply labelled as being a bit dim and steered towards a job which would suit your seemingly limited talents.

Thankfully things have changed. From being a barely recognised learning problem 30 years ago, dyslexia is now something which is closely monitored in schools, researched by scientists and boasts numerous support bodies and helplines.

A team of Finnish researchers recently found a gene which they said could be responsible for causing dyslexia, which again highlighted the considerable interest there now is in learning about and understanding the disorder.

But whatever the complex causes may be, one thing is for sure - it needn't necessarily limit your potential. Hollywood star Tom Cruise, Virgin tycoon Sir Richard Branson and British actress Keira Knightley are all dyslexic, and North-East artist Mackenzie Thorpe, who did badly at school and almost failed to get into art college because they couldn't read his application form, is now world famous for his paintings.

So what exactly is dyslexia? And how can we tell if our children, have it?

Carol Youngs, policy director of the British Dyslexia Association (BDA), says the disorder is difficult to define because it varies so much between people. In general terms, it means a difficulty with words.

''It's where their intelligence and ability isn't matched by their reading and writing skills. One young boy told me that when he looks at the page he sees the lines as waves and the words dragging down below the line. It's an almost visual disability,'' she says.

The problem dyslexics have is that their brains process information differently. This, the BDA says, affects the underlying skills that are needed for learning to read, write and spell.

An estimated four per cent of Britons suffer from severe dyslexia - those who find it almost impossible to read and write - and a further six per cent are moderate dyslexics, who struggle with the same skills, according to the BDA.

Tell-tale signs include a short memory, misreading, difficulty with sequences, poor organisation or time management and erratic spelling.

Dyslexia can't be cured, but as Youngs explains, people can learn to live with the disorder and minimise its impact.

Dyslexics can be taught to develop ''coping strategies'' for working around their specific learning problem. Youngs says many with short memories visualise memory maps which help them remember things by linking it to a specific image.

Technology has also played an important role in reducing the disruption dyslexia can cause to people's lives. Computer talk-back programmes, which read out what the user has written down, enable dyslexics to check their work without having to read it. Audio tapes also allow them to enjoy books, whilst spell-checks alert dyslexics to misspelt words.

But the biggest help a dyslexic can have is to be properly diagnosed in the first place.

Youngs says: ''An early pick-up is really important so the child can get extra tuition and help. If it's not picked up, children could keep coming bottom of the class, feel they're not good at anything and their self esteem goes down tremendously.''

Low confidence has been blamed for the relatively high numbers of prisoners and drug addicts with the disorder.

Researchers at the Scottish Drug Training Project found hundreds of addicts turned to drugs after they were made to feel outcasts as kids because of their difficulties with reading and writing.

A separate study found some dyslexics turned to crime after being ridiculed by their peers and because they were unable to gain qualifications or hold down a job.

Olympic swimming gold medallist Duncan Goodhew knows how difficult it can be for children with dyslexia. The breaststroke champion says he was seven when he first realised he had a problem, after a humiliating experience in front of his classmates.

''I stood up in front of the class to read and I had trouble with the words. The class thought that was very entertaining," he says.

''Being dyslexic is enormously frustrating. A lot of my friends were two-and-a-half years older than me so I was two years behind them in age and about four in academic terms. It's very confusing for dyslexics - they're very bright but unable to keep up in a classroom.''

But things have changed. Goodhew says when he was at school in the 1960s dyslexia wasn't recognised as a disorder and teachers were unaware of what it was and how to deal with it.

He explains: ''Now dyslexics are seen as people that learn differently, rather than as people with a learning disability. It's hard for people, but it's one of those things that either makes you or breaks you.''