It had been a bad day in the Year 1 classroom. Angi Hermann glared around at her class, squabbling, noisy, books spilled out over the floor. “This is not good enough,” she stormed. “You will all have to pull your socks up.” Startled, 25 out of 30 five-year-olds reached down and adjusted their footwear. Angi burst out laughing. “And all at once,” she says, “the mood changed. I read them a story and we all laughed at the jokes. Then they packed up and went home, all calm and tidy as you please.”

Angi would agree with Mark Twain (see right). Laughter is not only pleasurable, it is also a release from tension and a social bond. But for teachers faced with difficult children, pressures to perform and a curriculum to get through, a belly laugh may seem the last thing on the agenda.

Which is a shame because evidence suggests that laughing is good for you. In the current issue of Nature, researchers have even located the exact whereabouts of our sense of humour (somewhere in the left frontal lobe) in an area which also is connected with speech. It is a ticklish spot that when stimulated electrically can make a person giggle. But laughter is not only “aerobic exercise”, but also, as one American psychotherapist puts it, “an internal jog for which you don’t need to wear a special outfit”.

Other benefits claimed for a good giggle include stress-busting and a boost to the immune system, while the emerging specialty of psycho-immunology is beginning to produce studies on the protective effects of laughter in conditions like cancer, ulcers and bowel disease, heart disease and hypertension (high blood pressure).

So, is laughter the best medicine and would we all feel much better if we did it more often? Judging from the colossal number of entries on the Internet on this subject, lots of people out there think so. Dr Stanley Tan of the Loma Linda Medical Center in California for instance, who has studied the neurochemistry of laughter says: “Laughter brings a balance to all the components of the immune system.” And a new book, Mind-Body Medicine edited by Alan Watkins (Churchill Livingstone) confers textbook status on ideas considered way-out wacky only a couple of decades ago.

That’s when Norman Cousins wrote his path-breaking Anatomy of an Illness. In 1979, diagnosed with the excruciatingly painful spinal disease ankylosing spondylitis, he checked into a hotel room with a load of comic videos and Woody Allen films. Ten minutes of laughter, he found, would give him two pain-free hours. His next book, The Healing Heart (1983) detailed his recovery from a heart attack without surgery by using a raw food diet, exercise and - yes - roars of laughter. But that, of course, is in America.

The United States is not only home of the International Journal of Humor Research, edited by William Fry, emeritus professor at Stanford University; it boasts such organisations as the American Association for Therapeutic Humour in St Louis and the Humor Project at Saratoga Springs, New Jersey, which has given money to 25 therapeutic funnies over the past four years, and has psychotherapists in hospitals briefed to build laughter into their dealings with patients.

As Lisa Rosenberg at Chicago’s Rush-Presbyterian Hospital says of her work with sick children: “I’m a great believer in black humour. It is the ability to stare something scary in the face and say, ‘I can laugh at you.’ Laughter defuses fear.”

It’s not only sick children who need to laugh. From the time when infants first smile, at five to nine weeks, and chuckle - at about three months - children laugh an average of 300 times a day. Adults can barely manage 50, with real grumps dropping as low as six.

Every teacher knows what it is like to contend with a class rocked with sniggers at some idiotic joke and has felt sincerely with Anita Loos’s heroine in Gentlemen Prefer Blondes: “Fun is fun but no girl wants to laugh all of the time.” But equally, most adults could honestly admit to times when the innate merriment of most children uncracked their own reserve and left the whole room clutching their sides. Angi Hermann confesses to using laughter quite consciously with young children. “They know I am laughing with them. It makes them feel valued, that I enjoy their company.”

But how do you get to laugh if you are not naturally someone who sees the funny side of things? Writers advise developing your own humour profile, and keeping a supply of videos or books or cartoons which hit the funny bone.

Britain used to have a NHS laughter clinic, run by Dr Robert Holden and his wife Miranda in Birmingham. One of its suggestions for would-be laughers (500 on the waiting list) was to sit cross-legged in front of the mirror for two minutes everyday laughing at yourself. Research is said to show that fake laughter works almost as well as the real thing medically - though we all know how painful it is socially.

The Holdens no longer take the clinic and after a visit to India seem to have joined the UK Miracle Network, an interfaith mission where they offer glimpses to a transcendent joy beyond laughter, gained through letting God flood the heart with light.

Well, whatever gets you going . . . There’s a lot of that kind of ever-so-spiritual laughter on the Net. There are also a hell of a lot of jokes, mostly rather bad. Here’s one, for English teachers. “A man was very fond of wordplay. So he sent 10 puns to a competition in his local newspaper, hoping one of them would win. No pun in 10 did.” (Try saying it out loud.) Peter Gordon is headteacher of Hazelwood Infants School in Enfield, north London. He was an actor before he took up teaching and regularly goes around the classes performing magic tricks such as taking coins out of children’s ears. Recently the school had a successful Office for Standards in Education inspection, with 96 per cent of classes rated as satisfactory or above.

Mr Gordon sees humour as an integral part of making a school work. “We want the children to be happy, then they will learn,” he says. But what about the staff? With regular Friday lunches and a relaxed atmosphere in the classroom, teachers enjoy their lives, despite pressures. “Even after so many years, they still make me laugh,” says Year 2 teacher Jill Girling. “That’s part of what keeps me here.”

WHAT HAPPENS WHEN YOU GET THE JOKE

* We take in more oxygen, increasinglung capacity and ejecting mucus - this is good news for respiratory diseases such as colds, bronchitis or emphysema * Our blood circulation increases

* The stress-linked hormones cortisol and epinephrine decrease

* Blood pressure rises and then drops

* Muscles relax

* Neuro-chemicals called endorphins, (the body’s natural pain-relievers), are released

* Deep spasms as in arthritis relax

* Muscles, from the face to the belly, are given a good work-out

* Our moods get an “internal jog”, probably benefiting our immune system

* Our white blood cells proliferate; these are used to fight infection

* We feel more connected to our fellows