How trouble with words can spell a learning disability

There are many reasons why children fail to learn to read. Some households have no books and reading is neither encouraged nor regarded as a pleasure. In others, where English is not the first language, children may struggle.

But there are some children unaffected by such handicaps who still cannot master the written word. They are said to have dyslexia, which is described as a "neurobiological difficulty" by the British Dyslexia Association. Dyslexics have trouble processing words, which may affect their capacity to read and write, to name objects rapidly and to remember.

It is regarded as a specific learning disability distinct from other causes of reading difficulties, such as lack of intelligence or problems with vision or hearing. Many people with dyslexia are of above-average intelligence.

Signs of the disorder are erratic spelling, difficulty with getting sequences such as dates in order and poor organisation. Physical problems may include difficulty tying shoe laces or dressing. Many parents first become aware of a child's dyslexia when they fail to perform well at writing exercises . On the plus side, dyslexics tend to be innovative thinkers.

The condition is thought to result from differences in how the brain processes verbal or written language. Current theories suggest there is some form of defective or delayed brain maturation. Brain scans and post-mortem examinations have revealed differences in the brains of dyslexics, especially in the left hemisphere involved in reading. There is also growing evidence of a genetic link.

Experts disagree over criteria for diagnosis. Some say the condition should be redefined as a reading disorder, with the term dyslexia reserved for the 5 per cent of people with the most severe problems. The condition was thought to be more prevalent in boys but recent studies suggest it is equally common in both sexes.