It recommends that teacher education institutions and education authorities should pay more attention to the issue, and that students and teachers should receive more specialist help. Voice deterioration is a common symptom of stress.
The report notes concern from speech and language therapy specialists at the increase in the number of teachers being referred - and suggests this could be the tip of the iceberg. Teachers of PE, music and technology may face higher risks than others.
Voice clinics had an average of 5.2 teachers on their caseload during 1993-97, which rose to 8.2 at the end of that period, 15 per cent of those attending. This is estimated to have risen to 19 per cent. A third had sustained vocal damage.
A study four years ago found that a fifth of teachers took time off work due to voice problems, compared with 4 per cent of non-teachers. But the GTC report observes that not all teachers with voice problems will be seen by a specialist.
It adds: "Teachers who are unable to work due to voice problems are expensive in terms of replacement staff, and the experience is stressful for the teacher. Also it could affect the learning experience of pupils."
The problem is not just a familiar matter of colds and flu. "Teachers are required to use their voices constantly, above noise, often in environments where the acoustics are poor and where the atmosphere is too dry," the report states. The fact that many battle on in what is already a stressful job reinforces the pressures on their voice.
Employment tribunals have ruled in teachers' favour based on "irreversible damage to voice caused by the demands of teaching".
One female member of the GTC group which produced the report was referred to a voice consultant after she lost her voice and experienced considerable pain. She recovered after 11 months of speech therapy and says she has now learnt how to manage her poor voice days as well as prevent them.
* Pain when speaking or swallowing.
* A sore throat in the morning which disappears as the voice warms up.
* A hoarse, tired voice in the evening.
* An increase in mucus - especially if the mucus is not discoloured.
* Rapidly changing pitch or loss of voice control.
WHAT YOU CAN DO ABOUT IT
Warm up before prolonged use by humming gently or doing vocal exercises.
* Drink lots of water or juice.
* Breath from the diaphragm.
* Relax your shoulders and neck.
* Use a lower pitch or silence to gain children's attention.
* Ensure classrooms are well humidified using plants or a bowl of water.