“The worst moment,” said the teacher, “was casting the school play, Dick Whittington. One mother said that she wasn't going to leave until her daughter got the part of the cat. Forty minutes later she was still in hysterics, while her daughter was so embarrassed that she was curled up in the foetal position, weeping. To cap it all, the woman then turned to me and said: ‘Look what you've done to her!'”

Think of a victimised teacher and bullying parent and the scene that comes to mind is one of deprivation: crumbling temporary classrooms and knife-wielding students. But this teacher works for an independent London day school that is neither failing nor serving a deprived catchment area. In fact, it is one of an elite band catering for the children of the super rich. The buildings and facilities may be of a standard that most schools can only dream of but, as the new academic year dawns, teachers in private schools across Britain are bracing themselves to cope with parents whose behaviour can match anything you would see in an inner-city comprehensive. “Some of our parents could probably teach theirs a thing or two,” says a deputy head from a primary school deep in hedge-fund territory.

Wealthy parents may not threaten physical violence, but they can still be unnerving - and their weapons of intimidation far more sophisticated. Threatening legal action is a common tactic. One London school, for example, recently received a three-page fax from a top solicitor after parents objected to their child receiving a detention.

Even the smallest issue can spark a major confrontation. Dave Tenniel, the head teacher at a North London school, recalls one mother who stormed into the building after the morning drop-off because she disagreed with the way her child's homework had been marked. “She showered abuse on the form teacher and every member of staff. The deputy and I came out just as she was insulting the office staff, and she started on us,” he says. “Very gradually, we managed to walk her to the entrance and shut the front door.”

While that mother later wrote a letter of apology, plenty wouldn't. Not only are these parents unashamed about emoting on school premises, they consider it perfectly acceptable if it helps them to get their way. “A parent actually told me, ‘We reckon that those who scream the loudest get what they want',” says Tenniel.

Major independent schools, whose tradition and financial clout humble even the wealthiest of parents, are less affected. It is the small private day schools in the heart of cities such as Edinburgh and London that bear the brunt of the problem. Last week it was reported that even rugby, the “gentleman's game”, is suffering from bullying parents. The Rugby Football Union has circulated a code of conduct for spectators at its junior matches, with rules warning parents against verbally abusing match officials, intimidating players or spectators, and straying on to the pitch.

Nicholas Dorey, the incoming chairman of the Society of Heads of Independent Schools, says that teachers are increasingly being seen by the super-wealthy as employees: “As is the case with many other areas of society, teachers are being treated as servants rather than professionals,” he says. “There's a growing tendency for people to be vociferous, threatening and truculent until they get what they want. And if something goes wrong, it's got to be someone else's fault.”

Sam Freedman, a research director at the think-tank Policy Exchange and formerly head of research at the Independent Schools Council, agrees. “I've heard horror stories,” he says. “The type of people using independent schools has changed. They're not necessarily super rich but have a consumer mentality. They have the best TVs and expect to buy the best education. As the cost has gone up, expectations of what they're going to get have increased.”

Verbal threats may be just another form of bullying but, unfortunately, they work. There comes a moment when even the strongest teacher is tempted to take the line of least resistance. “We try hard not to give them what they want just because they have screamed at us but it can be really upsetting,” says Isabella Grierson, who teaches reception children at a pre-prep school in the Midlands. “You will do your level best not to experience it again.”

This reaction, says Dr Lesley Prince, a lecturer in psychology at the University of Birmingham, can be a symptom of a condition known as learnt helplessness. “You feel that, no matter what you do, you lose; there are no tactics that you can employ. It creates a kind of resignation or lassitude. It leaves teachers thinking, ‘What's the point? I can't stop them, so I might as well let them get on with it'.”

One result of the constant verbal batterings and solicitors' letters is that many schools feel powerless to intervene in the face of the less than idyllic aspects of their pupils' luxurious lifestyles. “Sometimes we don't see or even speak to some parents. The most you can hope for is their PA. I've ended up asking the chauffeur to tell the nanny to remind the parents that their son needs his violin the next day as his music lesson has changed,” says Janice Reddick, a form teacher in an Edinburgh prep school.

Some teachers label the phenomenon wealth deprivation: children who may be chauffeured to school,yet have no one in their lives who cares enough to teach them basic table manners. “I've seen eight-year-olds who don't know how to use cutlery because they've been given finger food all their lives. There are no set bedtimes and they're exhausted every day,” says Reddick. One of her pupils spent two weeks on a yacht off Mustique. “It sounds wonderful, except that the parents weren't actually there; they'd hired the boat and crew, who were strangers, and gone off to do something else.” Given the cases of teachers losingtheir jobs after parents kick up a fuss, you can't blame them for giving up. “In difficult exchanges an individual teacher can become a casualty because the school or its governors are swayed far more by the purchasing power of parents than by the justice of the case,” says Chris Keates, the general secretary of the National Association of Schoolmasters/Union of Women Teachers. “[Teachers] are intimidated if people say ‘I'm getting my solicitor involved'.”

No wonder that in some schools, parents seem to be ending up in charge. Some allow parents to collect their children at midday on Fridays - there's nothing like avoiding the evening rush hour to ensure that you make the second mansion in the country in good time. Others condone late pick-ups or last-minute absence for reasons that would provoke a riot in the state sector. “I remember one titled lady saying that she couldn't possibly collect her son on time because her tiara fitting was running late,” says Isabella Grierson. “Or we'll get a call saying that Conrad is going to be taken out for a portrait sitting and won't be back that day.”

Parents can seem to hold all the cards, so it's no wonder that assertiveness courses for teachers are springing up. Companies such as Impact Factory, which organise corporate training in everything from team-building to leadership, are reporting a growing number of inquiries from independent schools. For some, however, dealing with wealthy, bullying parents makes the job unbearable. “A head teacher I know retired early and said one of the main reasons was the pressure and distress caused by early-morning confrontations with the parents. He dreaded the bit when he would turn up at 8.15am before the start of school and get nothing but grief and aggravation,” says Nicholas Dorey.

Dave Tenniel's first year as head teacher was marred by his fear of demanding parents. “I'd go home at night and wonder who was going to wreck my day for me,” he recalls. “No matter how tough you believe you are, you can end up thinking, ‘I don't want to go to school tomorrow'. You try not to take it home but you do sometimes.”

Yet by treating teachers as lackeys and schools as just another service, parents fail to consider the message this sends out to their own families. “If children feel that the teachers are being undermined or devalued by parents, and that this behaviour is acceptable or normal, then it must surely rub off on their own attitudes,” says Dorey.

As the credit crunch bites, holding out against parent power is a course that may require even greater courage in the future. Some schools fear a full-scale retreat from the private sector by the middle classes, leaving the über-rich increasingly in control. Indeed, it may already be starting. One teacher sends her daughter to the school at which she teaches, paying heavily reduced fees. When she complained after her child was attacked by another, the son of a City mogul, she was told that he would not be punished. “They're paying; you're not,” was the reason given.

“Forget SATs,” says Tenniel. “Our problem is that however hard we try, the only thing some of our pupils are learning is that school is a waste of time. All you need is money, threats and a good lawyer and you can get anything you want.”

Some names have been changed.

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