Lesley Wright looks at teenagers going to cinemas and parties, experimenting with different make-up and clothes, different friendships, affectations and pastimes. She feels envious, for her daughter has ME (myalgic encephalomyelitis) and has been cloistered at home for the past three years. “If Lorna were with them, I perhaps wouldn’t like half the things she’d be doing, but at least it would be normal,” she says.

Morag Marston, who works in the evening, watches teenagers overtake her on roller blades. “I want my daughter to be doing that” - but Trudi, who also has ME (now more accurately described as chronic fatigue syndrome) has been stuck at home for the past year. The 14-year-old’s only excursions are to the doctor’s surgery.

These two girls, both at Largs Academy, are among the five known cases of pupils in North Ayrshire whose condition means they are receiving regular home tuition. Mary Davidson, assistant principal English teacher and guidance teacher at the school, teaches both pupils and is - like their parents - conscious of their loss. “They’re missing out on interaction with other kids, all those friendships that they form and lose at this age, all the things that socialise us.” A few of Trudi’s friends still come in to see her at lunchtime.

Lorna, who is now 16, has found her friendships petering out. She couldn’t accept invitations to do the things her peers do. Now she feels so estranged she cannot imagine going back to school. Her mother believes that even if she were to return, the mental gulf between herself and other pupils would be significant.

But any talk of a return seems academic when she sometimes feels too weak to get out of bed, so her one hour of tuition a week has to be cancelled. For the foreseeable future Mrs Davidson is - like other teachers who agree to take on home tuition as well as their staff job - the main link between pupil and school. She tries to think of small ways of keeping the link alive, such as inviting a home pupil to contribute to the school magazine. She would like to see more - perhaps an occasional excursion to the school library for an hour on a day when the pupil feels strong enough. She sometimes believes the increasing isolation experienced by many ME sufferers prolongs the condition. “Some doctors believe it is a depressive illness. I wonder whether feeling low is more a symptom brought on by the isolation and the sheer and utter boredom. ”

Morag Marston is emphatic that CFS is not a form of depression. “Trudi is not crying. She keeps herself going. It is very upsetting when people say it is all in the mind, let her get on with it. If they could see her trying to walk round to the doctor’s and her legs refusing to work. We have to stop for a while, two or three times.”

Last year physicians, psychiatrists and GPs from the medical royal colleges agreed the affliction was real, but said its causes were a mixture of physical and psychological factors. They recommended the new term chronic fatigue syndrome (CFS), as the condition is characterised by long periods of weakness and lethargy.

The cynicism of friends and medics is an extra burden for patients and their families. The Marstons first realised Trudi was unwell when she vomited in the queue for a ferry in Ireland. They put it down to heat or travel sickness. But she has carried on vomiting from time to time, between periods of exhaustion. Her mother was embarrassed to have to ring the school repeatedly and say her daughter was not coming in - without a name to describe her condition.

At the medical practice Mrs Marston was told that her daughter was suffering from viruses. Disconcertingly, she was asked whether the cause could be school phobia, pregnancy or drugs. After months of visits and tests the family finally got a diagnosis. Anything seemed better to them than simply not knowing what was wrong - the weakness, paleness and vomiting had made leukaemia their private fear.

The school had already decided that Trudi was ill. A teacher who had recovered from a similar condition recognised her predicament and sometimes gave Trudi notes, so that she could withdraw from a class and rest. Her guidance teacher finally told the family not to attempt to send her in, even for short spells.

Many schools and doctors take a long time to realise there is a problem: they look at the pupil and the failure to present homework, and for some time presume it is a lazy or hypochondriac child. “You read about so many other schools where they don’t entertain it at all. They tell pupils to get back in there,” says Mrs Marston.

Big efforts are being made to try to ensure that Trudi keeps up with her friends in school and does not have to repeat a year. Four teachers each come for an hour a week to coach her in French, mathematics, geography and English.

The hour-long one-to-one lessons are concentrated - although an inability to concentrate for long periods of time is one ME symptom. Mrs Davidson confesses to finding the hour-long lesson with no interaction or input from other pupils draining for her too. She has no trouble in identifying how hard it is for her home tuition pupils. “Before I did this teaching I might have wondered whether pupils claiming to have ME were trying it on a bit. I don’t know what ME is now, but I do know that it exists. Halfway through a lesson you can see the strength go from them and the colour drain from their face. We have to stop.”

Lorna Wright triumphed with a 2 in English Standard grade last year, but this year, despite submitting portfolio work, did not feel strong enough to deal with the day-long Higher exam. Pupils are given extra time for each paper - about an extra 45 minutes for a one-and-a-half hour paper and are allowed to sit the exam at home, but it is still an ordeal.

Both families are living day to day with not knowing what causes ME and when their daughters will get better. They cannot make plans for outings or holidays - the whole family is affected by unpredictable weeks, days, hours.

Lorna’s condition has now improved a little. Most days she can get out for a short while. Having got to know another CFS sufferer four miles away, the two occasionally embark on a trip to the cinema or swimming pool. The improvement may or may not be related to experiments with a wheat-free diet and dietary supplements, but the family is in no doubt that she has been helped by getting to know someone in a similar position.“I don’t know what we’d have done otherwise,” says Mrs Wright. “I’d advise other families to keep on looking until they get support from whatever quarter.”

Getting to know another family hit by CFS has also made a big difference to Mrs Marston. “You feel cut off and on your own. I was so pleased to meet up with another mother who really understood.” She watches Trudi, once an enthusiastic basketball player and horse rider, live a vicarious teenage life watching Australian tv soaps. For now, the teenage years are on hold.

WHEN THE TEACHER VISITS HOME

* North Ayrshire introduced a home tuition policy this session. There are about eight cases at any one time. When a child is absent for more than four weeks, and if he or she has medical evidence, the school is required to start tuition. This is usually provided by its own staff after hours on a voluntary but paid basis. If not enough teachers volunteer, staff have to be found elsewhere.

* For a free information pack on CFS, write to Department 200, Action for ME, POBox 1302, Wales BA5 2WE. The UK MECFS helpline is on 0891 122976. Local support groups: Aberdeen 01224 307918; Dundee 01382 76460; Edinburgh 0131 337 3531; Glasgow 0141 204 3822