You've got to be firm but fair, keep your sense of humour in the face of extreme provocation, and get used to young men questioning your parents' marital status. Yes, teachers have a lot in common with football referees. Ted Wragg (below left), himself a qualified referee, meets David Elleray, the Harrow schoolmaster who's just turned down a trip to the World Cup because his pupils need him.
Here's an offer: four weeks off school, to be spent in France in nice hotels, with all expenses paid and a few World Cupmatches thrown in. Irresistible, isn't it? Well, I've just met the madman who turned it down because he didn't want to miss his geography classes.
David Elleray leads an unusual double life: head of geography and house master at Harrow School during the week, Premier League referee at the weekend. When I was a schoolboy at King Edward VII Grammar School in Sheffield, we were in awe of our head, Dr Barton, not for the well-known physics books he'd written, but because he had refereed an FA Cup semi-final.
Not many teachers have managed such a tricky combination. It requires discipline, determination and flexibility. Philip Don, the London head who refereed at the last World Cup, is one who did it, though he has just left teaching after 25 years to become the Premier League's first referees' officer.
Visiting Harrow School is like taking a journey back in time: no girls, masters in gowns. The only shop in sight is the Harrow School Outfitter, right next to Druries House, where David Elleray is responsible for the pastoral care of 60 pupils. A sign in the shop window announces "Shoe repair service here". It's reassuring to know that toffs don't just throw things away when they're damaged.
David Elleray's study is a fascinating mixture of traditional and modern: wood panelling, a bowed bench seat along the window, reference books, a word processor, a croquet set and squash racket in the fireplace, a photograph of the cast of the house play.
It is the other artefacts that catch the eye, however: a pennant from a Barcelona FC match; a photo of Paul Ince in Manchester United kit, looking none too pleased at an Elleray decision; another of Mark Wright and two other Liverpool defenders pointing in one direction, Elleray with both hands raised ("I was about to send Grobbelaar off for handling the ball outside the area. They're pointing at the linesman''. "So what did you do?" "I went over to the linesman and he said he had flagged for offside, so I gave an offside kick"); Elleray waving a yellow card. Then there is a scene that all players dread: Elleray holding the red card aloft. Early shower for you, sunshine.
Refereeing and teaching have a lot in common. Both involve applying rules, making quick decisions, dealing with problems, understanding human beings. Teachers, fortunately, do not have to listen to 30,000 spectators booing their decisions, questioning their eyesight, or chanting "Who's the bastard with the chalk?". David Elleray has the darting glance of a man well used to evaluating situations, both in the classroom and on the games field.
Harrow has a footballing history, though rugby is bigger there. David Elleray talks with pride about Charles Alcock, founder of the Football Association and the FA Cup who was a pupil at Druries House in 1855. Alcock based the FACup on Harrow's inter-house competition.
Like many teachers, I qualified as a referee so that in an emergency I could take over a school or university game, but David Elleray's story is quite different. "I started refereeing at the age of 13 at Dover Grammar School. I decided I wasn't going to make it as a player, maybe the school second XI at best, so I became a referee instead."
A 13-year-old refereeing men's games in the local league is unusual, but David Elleray had even loftier ambitions. "I decided, when I was 13, that my ultimate ambition was to referee the World Cup Final in 1998," he says. Thirty-one years later, the dream will not now come true.
As a student at Oxford he refereed games and ran the inter-college programme. After university he became a geography teacher at Harrow. He carried on officiating in non-league football before making it on to the Football League list, progressing eventually to the Premier League, European competitions, and international matches.
David Elleray has organised his life to get to the top. Referees run about eight miles in a game, often at top speed when play switches rapidly from end to end, so he has to be very fit. International rules require him to be able to run 2,700 metres in 12 minutes, after four shorter sprints. Never one to settle for the minimum, he does more than 3,000 metres in training.
"I don't smoke. I drink very little," he says. "I have to be an expert at time management. I rely on the boys behaving well when I'm away, or I'd have to give it up. Fortunately I've got a very good deputy housemaster".
He also has to be able to cope with extreme pressure. "I had to give two penalties against Chelsea in the 1994 cup final. The first was clear cut. The second was harder to give, but I had to give it. I've always been a strong referee, not one to make 'diplomatic' decisions. If you've just given three free-kicks against the home team and someone else commits a foul, then you have to give the fourth free-kick. You have to stand by your principles."
The press love to call him a "schoolmasterly" referee, a label he dislikes, because it is used as a synonym for "pedantic' or "fussy" by people who do not understand teaching.
He does, however, see many parallels with teaching. "You're dealing with people, so common sense is important. Both boys and players try to test the limits to see what you'll stand for.
"I'm a strict teacher and a strict referee. Sometimes you have to spot a potential troublemaker early and take action before things get out of hand, but you've always got to be fair. And you have to sacrifice short-term popularity for long-term respect. Reputation helps, both in refereeing and teaching."
None the less, he keeps the two worlds as separate as possible. "Sometimes, if you've had a bad day at school, it's a nice change to go to Old Trafford and get roasted by 40,000 spectators.
"There's a lot of pressure on referees. People don't expect Alan Shearer to score with every shot or David Batty to win every tackle, but they do expect referees to get every decision right.
"It's only if things go badly in a game that I move into 'absolute bastard' mode. And I always try to avoid any frustrations from a match spilling over into the classroom. It wouldn't be fair to take it out on the boys."
Does he ever have a joke on the pitch? "Oh yes, but usually at my expense, not the players'. Tony Adams (of Arsenal) called me a cheat, so I replied, 'We may be useless, but we don't cheat'. Dennis Wise (of Chelsea) is a fiery player, but he has a good sense of humour; you can joke with him. You can't be in teaching without being teased. The boys love telling me what I've been called by television commentators. The ruder it is, the more they enjoy it."
So, 31 years after he set out his lifetime's ambition, 1998 has arrived. He has all the credentials, having impressed the world's top administrators. "I refereed a so-called 'friendship' game between Germany and Brazil and had to book three players in the first five minutes. Then I sent off a German player and the Brazilian captain. But they invited me to go to Brazil and referee a competition final in front of 100,000 spectators."
Last month, with Harrow's usual blessing, he flew out to Brazil on a Friday, refereed on Sunday, then flew straight back so he could be at a parents' meeting on Monday evening.
He is unashamedly ambitious for himself and his pupils. "I am a hard taskmaster, but I want them to do their very best, for themselves and their families, and I want Druries to be the best house." He calls himself a 24-hour-a-day workaholic, and seems to me to have an extraordinary drive to achieve. So why, why, isn't he going to France to fulfil his childhood dream?
"Professionally, I couldn't do it. These boys have got A-levels, GCSEs and we've got next year's intake doing the common entrance exam. They're at Harrow for five years, and I couldn't be away for the end of term when they come with their parents to say goodbye. I didn't even have to think about going. It would just be wrong." A lifelong ambition ditched at a stroke, a striking example of teacher dedication. "Quite remarkable," as John Motson might say.
David Elleray cannot referee international matches after next year, when he reaches 45, so he really has given up his only chance of going to the World Cup. In 2003 he will have to finish with the Premiership, but he still has ambitions: he wants to be a headteacher. I liked and admired him, so I hope he fulfils this ambition, having sacrificed the more glamorous one.
A couple of weeks before I did this interview, I bumped into one of our local league referees in Exeter. He often referees university games and is invariably firm but fair. "I'll be meeting David Elleray soon," I told him.
"David Elleray?" he replied. "He's the best." Then he thought for a moment, no doubt consulting some invisible linesman. "Yes," he went on, "no doubt about it, he's the very best."
Never argue with a referee.