Teachers’ voices are their indispensable tools, used constantly not only to pass on information, but also to cue an emotional context for it. But whereas other professional voice users, such as actors or singers, are trained to extract maximum performance from their vocal cords with minimal risk of damage, teachers have been left to shout and croak with little guidance.

As a result, hoarseness, sore throats and sometimes protracted voice loss are familiar complaints in many staffrooms. At least one teacher, who began to lose her voice when her class size was increased to 44, succeeded in having her complaint recognised as an industrial injury. Noisy open-plan classrooms can also aggravate voice problems.

The vocal cords are a pair of mucous-coated muscles at the top of the windpipe that vibrate when air is blown through them from the lungs. These vibrations, 100 per second in men and 200 per second in women, are the sound which, when it has been shaped by various parts of the mouth, we recognise as speech.

The whole apparatus is smaller than a postage stamp. Like other muscles, the cords can be strained or torn, which in turn causes the 40-odd other muscles supporting them to ache. They also blister when they rub against each other, and these blisters can become fibrous nodes that may have to be removed surgically.

Moira Little, speech and language therapy manager at Edinburgh Royal Infirmary, advises teachers to warm up their voices by singing along to the radio in the mornings or by humming, an exercise which can become part of the class’s routine. You can keep the vocal cords moistby sipping water. In class, try methods such as clapping patterns to attract attention, so saving your voice.

Most important of all are breathing and posture. Pain and injury occur when your throat muscles do work that your chest muscles should be doing. Sit or stand comfortably straight, relax, and take deep breaths so that a full, steady stream of air is expelled through the vocal cords.

Stress contributes to voice loss by tensing the abdominal muscles. So does lack of confidence. Robert Palmer, head of voice at the Royal Academy for Dramatic Art, says that “intention is 90 per cent of good projection. I have heard actors whispering successfully to the back of an auditorium, mainly because they were determined to be heard.”

Avoid throat lozenges, he says (menthol, a common ingredient, actually dries the throat) and instead breathe steam from a bowl of water under a tea towel. His other tip is to rest the voice completely when it starts to give way. “I know of West End actors who are communicating with their families with notes on Sundays.”

A few years ago, a survey found that one third of voice therapists’ patients were teachers. As a result, Roz Comins set up the Voicecare Network, a charity, to educate teachers about voice care and use. The network now has 100 experienced tutors who are prepared to hold workshops for groups of teachers in schools. For a list, contact The Voicecare Network, 01926 864000, or write to 29 Southbank Road, Kenilworth, Warks CV8 1LA. The networks booklet, “More Care for Your Voice”, costs pound;4.50 from the same address. And if all else fails, megaphones are available by mail order from Newitts, 01904 468551.