It is estimated that 5 per cent of children have serious problems with dyslexia and another 20 per cent are affected less severely. It is helpful if teachers are aware of the difficulties these children experience, so that they can plan and set learning targets.

When a child has literacy problems, the first step is to check hearing and vision. Dyslexia is not the only cause. Children start reading late for a variety of reasons, including illness, being young for their year, misunderstanding the process, or simply lack of practice. With sufficient directed exposure to print, many children will get going in the usual way. Children with below-average ability will also take off in a normal way phonetically, but at a slower rate, and they may need help to follow storylines. All children need practice in reading and writing. Most children reverse some letters and numbers at first. However, in dyslexia this may continue beyond infant school.

Scientists in Oxford, Professors John Stein and and Tony Monaco, earlier this year reported evidence for an hereditary component in dyslexia associated with the genes controlling immunity. They speculate from their findings that something wrong with the mother’s or unborn child’s immune system could have an effect on a vulnerable line of brain cells called magnocells. Magnocells are involved in timing and co-ordination, registering tiny modulations in sound and in flickering images.

If the magnocell system is made less efficient, sequences of subtly different sounds will be less efficiently processed. Indeed, most dyslexic people have difficulty segmenting sounds within words and miss out syllables. They may also have difficulty with sounds such as “b” and “d”, which have very similar sound modulations.

Dyslexic learners tend to plump for dealing with words as whole units. They rely on (sometimes large) sight vocabularies to progress in reading. They may substitute words that look similar, or guess wildly from the storyline. Since they are not building up recognition of detailed sound patterns inside words, they miss out on the associated visual detail. This means failing to build up their memory store of the detailed spelling templates most children have ready to compare with what they read and write. Without this self-checking facility, dyslexic writers seem unaware of mistakes, or may simply appear to be rather careless. Many children with dyslexia only begin to notice detail in reading when they are taught to spell. Problems with spelling may look visual, but can usually be traced back to problems in processing a stream of sounds.

But there can be visual problems too, such as not noticing the difference between “n” and “h” - although this is usually seen in young children or those with severe dyslexia. One visual problem hard to deal with is flickering images, also related to the function of magnocells. On a computer screen or page, the images flicker. Dyslexic readers miss out or add words, and lose their place. This can be mistaken for carelessness.

There is a high correlation between hearing loss and dyslexia: up to 70 per cent. A small percentage also have eye problems, such as poor eye convergence. Again the magnocells are implicated, as they contribute to efficient small muscle control, as in tongue and eye movements. Alexander Faludy, the youngest boy ever to win a place at Cambridge, has such severe eye convergence problems that he is unable to read a text without a taped version. There is also some relationship between dyslexia and handedness or being ambidextrous.

Help often involves speech therapy. A child usually grows out of speech problems, but may have more subtle difficulties. For example, we often say words under our breath to analyse the sounds, and to memorise items. Since people with dyslexia do not use this memory tool, they have difficulty with anything that is traditionally learned by saying a sequence, such as days, months or tables.

Problems also arise with memory. Although a dyslexic pupil may know the concept or meaning of a word, the name can escape them. “You know, that thingy” often crops up in conversation. They will need practice to name the letters of the alphabet fluently. Arbitrary pair labels such as “left”, “right”, and “quarter to” and “quarter past”, can also cause problems.

“He’s not dyslexic, he’s just a bit slow writing things down,” is sometimes given as an explanation. In dyslexia there is often a slightly slower rate of integrating and processing information. Although quality of thought is not affected, the writing often is. This often shows up in copying from the board: the pupil will need extra time to finish.

Listening skills may be affected. The child may seem inattentive or forgetful, and young children may get so out of step they seem to be deliberately misbehaving.

Professor Stein points out that dyslexia carries some advantages. Many people with dyslexia have above-average visuo-spatial skills and show talents in art, drama, certain kinds of problem solving, and architecture. Some excel in the type of visual reasoning needed in higher level maths. Einstein had problems with arithmetic and was twice sacked from teaching for poor spelling. Some experts consider dyslexia to be more a learning style than a problem. In China, where language has pictorial symbols, dyslexia is not recorded.

Dyslexia can affect children of all levels of ability. When a child is bright verbally but not reading, underperformance is evident. But many children have their potential hidden by their dyslexic difficulties. Dyslexia needs to be considered when investigating behaviour problems. Without support in a reading environment, a child with dyslexia can feel a lot of stress. and may turn to depression or aggressive behaviour. But if the condition is identified, appropriate multi-sensory teaching can enable pupils with dyslexics to fulfil their educational potential.

Specialist provision, however, remains a thorny issue.

IS IT DYSLEXIA? SIGNS TO LOOKS OUT FOR:

* Family history

* Speech, eye or ear problems

* Missing out syllables, inability to segment sounds in words

* Mixed or lefthandedness

* Difficulty in learning alphabet names and sounds

* Reversing letters after age six

* Failing to read or write

* Apparent underperformance in literacy compared with general ability

* Bizarre or over-phonetic spelling

* Slow reading, voice pointing, wild guessing, missing words or lines.

* Difficulty in recalling names of things

* Slow and inaccurate copying

* Forgetting instructions

* Items learned seeming to be lost

* Poor arithmetic

* Difficulty with sequence of small events as in learning to tie laces

* Difficulty remembering sequences such as days, seasons

* Tuned-out appearance, inattention, forgetfulness with instructions

* Depression or aggression about learning

* Notable visuo-spatial strengths