The reason I started my consultancy, Pronunciation Matters, was because I saw a 'niche' whilst working as a teacher for the State government run Adult Migrant English Program. I was working in the industry program and low level literacy students were being replaced by high level skilled migrants who had a good command of English but needed work on pronunciation and listening to fast 'Aussie speak'.
Two years later my idea is successfully continuing and I have worked with overseas trained scientists, teachers, engineers, IT workers, accountants and customer contact employees. They are all working at their professional level or just below. After a five or ten week intensive program they are well on their way to becoming much more confident with their communication at work.
The idea is not to get rid of their 'accent'. Accents are good and make life interesting. The main purpose is that their pronunciation 'errors' do not interfere with meaning. Some people, of course want to lose their accent. This requires a lot of work and practice.
This brings me to the other important issue about pronunciation training and that's practice followed by practice and yet more practice. You are 'unlearning' your mistakes and learning new skills so like any new skill you need to practise and listen to recordings of your speech.
Finally, the other important issue in pronunciation training is that initially your speech will become worse before it gets better. This is because you are breaking the cycle and introducing self correction. You are also focusing on what you can't do instead of what you can do. This becomes very frustrating and you may feel that your English is not as good as you thought it was. This will pass with a lot of (you guessed it) practice.
