Now Karen has been wired for sound; her room is fitted with an amplification system developed for schools. After three weeks she is already noticing the difference. "My voice is improving; it isn't strained by using the system. Now I would feel lost without it."
Bordesley Green is one of a growing number of schools using sound-field amplification in the classroom. Speakers placed around the room are connected by radio link to a small microphone worn by the teacher. Users of the system claim that, as well as allowing every pupil to hear, it makes classes easier to manage and reduces stress.
Its main supporters go even further, claiming that it will transform teaching and learning. David Canning, educational audiologist at London's City University, has pioneered the introduction of sound-field amplification into British schools. A former teacher of the deaf, he first saw the system working in the United States and saw it as an aid for hearing-impaired children.
A year ago he approached BioAcoustics, a company based in Luton, Bedfordshire, that provides electronic solutions for noise, speech and hearing problems, to tailor a system for classrooms. The system was trialled in 13 schools, with the aim of testing its effect on children's listening and behaviour.
Mr Canning says: "It's everything it seems to be: the power to change classrooms in a positive way with little effort and little expense. We have reduced vocal load and strain on the teacher's voice. It has improved the teacher's performance in the classroom. And children can hear better.
"Teachers found children spent more time on task, and they spent less time managing the children. Children were more productive and paid attention for longer."
Following these findings, London University's Institute of Education is to conduct its own study at a school in Luton. Nick Peacey of the institute's special educational needs joint initiative for training, says: "If this system is up to scratch, we will get a system developed because of concerns about special needs but which will include everyone in class."
So how does it work? Andrew Streets of Bio-Acoustics says sound-field amplification does not substantially increase the volume of the teachers' voice. Rather, it has an almost subliminal effect. "It creates a sound field that enables children to hear wherever they are."
The borough of Camden in north London has installed 10 systems in primary schools to help hearing-impaired pupils. Jo Keyte, Camden's advisory teacher for deaf and hearing-impaired children, says: "Sound-field amplification doesn't just pinpoint the hearing-impaired child; hearing children benefit as well. We have had teething problems. At first we went for microphones that fitted around the head. Some people found that intrusive, so we changed to lapel microphones. But it should give children much better access to the teacher's voice."
Karen Roberts from Bordesley Green has discovered other drawbacks. "I jokingly asked the head for a new suit with pockets. Sometimes it's a problem having nowhere to put the microphone pack.
"And the on and off switches are minute. I have been caught out, going out into the corridor and forgetting to switch it off. You start chatting, come back and find all the pupils have heard you."
But, she says, the advantages far outweigh such inconveniences. "It makes you far more aware of what you're saying. And I no longer have to project my voice or repeat myself so often. Overall, it has been a major plus. After all, a lot of teaching isn't what you say; it's how you say it."
The basic classroom system from BioAcoustics costs Pounds 949, and the more powerful system for a school hall is Pounds 1,385, both plus VAT and including installation. Contact BioAcoustics, tel: 01582 431000