If I want to learn American English,I should learn form an American teacher or my English will not be understood when I go to the U.S.A.
I have seen many good teachers here in China,both expatriates and Chinese,run into problems because of the way many students judge their accents. Students believe that the best chance of speaking like a native speaker is by having that ideal accent. If the teacher has an accent that is not form the target country that certain students want to go to,they are either rebuffed12 or rejected.
Part of the misconception stems from ignorance of the distinction between pronunciation and accent. Pronunciation involves the stress,rhythm,intonation,and phonetic sounds that facilitate communication. An accent is the distinguishable set of sounds that derives from cultural or regional phonetic patterns. Accents are essentially habits formed at a very early age and very difficult to change after the age of six. This has been verified13 by researchers who studied the tongue and mouth positions of Israeli children at an early age of 5-6,and find that even after heavy immersion14 in American English for about 10 years,their mouth and tongue positions change very little when speaking,and thus their accents change only slightly. In other words,forget about trying to change your accent in a year or two,it is just not going to happen. Pronunciation can be changed and improved. Accents are entrenched15 and need not be changed.
There is no shortage of superb English speakers and writers in my native country,Canada,who have excellent pronunciation,but heavy accents from their countries of origin. In fact,two great Indo-Canadian writers Michael Ondaatje and Rohinton Misty both have slight non-Canadian accents in English,but are Booker Prize16 winners. Do we say that their English is substandard,because they have accents？ No,it would be absurd to make such a suggestion since their pronunciation is excellent and no one has any trouble understanding them. As I mentioned earlier,pronunciation is not the same thing as an accent.
I tell my students to give up their hope of developing an American accent,since it is very unlikely to happen unless they stay in America over a very long period,and even then,the are still likely to retain some part of their Chinese accent. An accent is par of your character and heritage.
That is not to say that the student shouldn't devote time to improving his or her pronunciation. A student should focus on those pronunciation aspects that make their communication more effective,not trying to mold their accent into another. Developing pronunciation skills that are universally learnt is a much more worthy pursuit of your efforts than trying to copy an accent that is unnatural for your tongue and mouth.