Headteacher Martin Haworth has a recurring fantasy about an intruder who walks into school while he is taking assembly.

When he realises that his pupils are under threat, he throws off his teachers’ gown with a dramatic flourish.

“I leap into the air with a long kick,” he said. With a black belt in karate, the head of Wallington county grammar, in Surrey, is a master in the art of self-defence. “I can defend my boys if I need to.”

But karate can also be a helpful classroom-control technique. “Karate gives you a certain presence. You use specialised techniques. You know how to kill. Pupils don’t mess with me.”

Mr Haworth’s black belt is one of the aspects of his school mentioned in the Good Schools Guide, which has just published its 2006 edition. The guide is compiled by editors around the country, who submit information on their local schools. It includes entries on more than 800 state and independent schools.

Among the lists of academic achievements, sporting facilities and artistic activities included in the guide, each school’s entry offers a description of the personal attributes of the head.

Ralph Lucas, publisher of the guide, said: “Heads set the style for a school. From the chaotic to the organised, a head can change a pupil’s experience quite radically.”

So parents seeking a warm, welcoming school, might choose to entrust their daughters to the care of Mary Morris, head of pound;3,230-a-term St Helen’s, in north London. Talking to Mrs Morris, the guide suggests, is “a bit like talking to your best friend”.

But friendliness is a difficult line to tread. The guide’s description of Mr Haworth’s neighbour, Wallington high, suggests that headteacher Barbara Greatorex inspires devotion verging on the cultish: ”(She is) always surrounded by smiling girls when she walks around the school.”

But Ms Greatorex said: “It makes them sound as though they’re on drugs.

They don’t follow me around. But they don’t cower when I go past, either.

“I like to think the girls can come and talk to me. I’ll sit and have lunch with Year 7, and they have no qualms about starting a conversation with me.”

Others aim at gravitas, without necessarily succeeding. Describing Michael Gormally, head of Cardinal Vaughan boys’ comprehensive, in west London, the guide states: “We wanted to describe him as giggly, but he would prefer to be jocund.”

And Tim Hastie-Smith, head of pound;7,495-a-term Dean Close, in Gloucestershire, is described as “dashing”, in lilac shirt, purple-patterned tie and orange and turquoise socks.

“How you dress is an expression of who you are,” he said. “It’s about trying to be approachable and available.

“It’s so easy for a headmaster to be a chief executive, working from an office and never seeing the kids. But it’s about being an accessible human being as well.”

Several boys’ school heads strive to convey an image of authority. Anthony Jarvis, head of St Olave’s and St Saviour’s grammar, in Kent, is presented as “authoritative, without being intimidating. A busy man”.

Many heads clearly hope that looking busy suggests efficiency. The entry on Peter Hamilton, head of pound;3,200-a-term Haberdashers’ Aske’s, in Elstree, Hertfordshire, is accompanied with a list of his hobbies: canoeing, mountain-walking, riding, sailing, karate, classical music and comparative literature (“when time allows”).

“Lots of fresh air is absolutely essential,” said Mr Hamilton. “If you’re riding a horse across mountains, you need to concentrate on that, rather than on anything else. It clears the mind wonderfully. And you have to be efficient. It’s the old-fashioned idea of healthy mind and healthy body.”

But, despite his efficiency, he reserves many of his hobbies for the school holidays. “In term-time you’re limited,” he said. “It’s just the gym and good intentions.”

In contrast, some heads’ entries contain no hobbies or character traits, and are nothing more than a list of qualifications. “Sometimes they’re new in the job,” said Lord Lucas. “But sometimes we can’t think of anything interesting to say about them. You don’t need to be brash and colourful to be a head. But there are some boring heads out there.”

Book of the week, Friday magazine 18 www.goodschoolsguide.co.uk