Patricia Clowry, a primary school teacher for 19 years at Sneyd Green, Newcastle-under-Lyme, began to lose her voice in 1988 when her class size was increased to 44. She needed three operations to remove nodules on her vocal cords, and had to leave the profession.
An industrial injuries tribunal ruled last month that she was entitled to a disability pension. The amount has still to be decided.
Mrs Clowry said she had heard of many similar cases since she began her battle. "Too many to mention, it's a bit overpowering."
Brian Carter, Midlands representative for the National Union of Teachers, said there had been an increasing number of cases.
Frances Oldfield, a former primary school teacher on Merseyside, lost her voice in the summer of 1992 and was forced to retire early. She is pursuing a civil claim against Knowsley council which is due to come to court in April.
Mrs Oldfield also had an operation to remove a polyp, but her voice has never completely recovered. She believes the background noise in her open-plan school was a key factor.
Roz Comins, who co-ordinates the Voice Care Network, an umbrella group of nearly 200 people, half of them experienced speech therapists and voice teachers, said one in 10 teachers could expect to have a problem at some time. But a third of teacher training institutions now run courses on voice care. Ms Comins wants the Teacher Training Agency to ensure they are offered to all students. Heads should be aware of noise problems and voice awareness in managing their schools, she added.