How to explain accent variations to students

OK, there are a couple of things that you need to tackle initially:

• if students have it into their head that there exists one single accent that is "the correct" one, then you need to start by educating them on that point: explain to them that no two people have a precisely identical accent, that the associations we attach to different accents are purely arbitrary, and that even within what is perceived of as a "standard" accent (e.g. among TV newsreaders) there is actually variation -- as an exercise, maybe you could have the students listen to some different newsreaders and look out for differences, e.g. in the vowel used in "path" etc, whether they pronounce the first syllable of "decided" with a schwa or a [I] vowel etc;
• given that, they need to understand that hearing one example recording gives them a typical pronuncation "within certain parameters, subject to some variation";
• students need to understand that a phonetic transcription is an abstract analysis, where the transcriber attempts to give "the main features" of an utterance, and in the case of a dictionary, not even an actual utterance but an imagined one; they can't expect to even glean all of the details of an actual pronunciation from a transcription, let alone then use that as a judge for all utterances of a given word/phrase.

Things that may help you:

• the Speech Accent Archive -- as an exercise, get the students to listen and note differences of various pronuncations deemed to have a given "accent" (some have phonetic transcriptions -- these could also be used as support)
• work by Peter Trudgill on perception of accents (sorry, don't have exact ref to hand, but he compared foreign speakers' reaction vs native speakers' reaction, showing that perceptions of accents are arbitrarily learnt rather than inherent)
• the book "Urban Voices" by Foulkes et al
• a little bit technical, but if you don't mind paying for it or local library has access, Emmanuel Ferragne & François Pellegrino's article "Formant frequencies of vowels in 13 accents of the British Isles" in the Journal of the IPA (2010, vol 1) -- even if you/they don't understand all the technical details, it may serve visually to say "look, there are quite a lot of differences between accents"

It seems to me that the most sensible way to head off these problems would be to explain to the class before doing any spoken English work that there is no such concept as "Putonghua" for English. While it may be OK for China, which has traditionally strived to be a rather centralized society, English has its major cultural centers diffused all over the globe.

There isn't even really a kind of "central accent" you can work on. Probably the best thing you can do is to try to give them yours. So even if your students manage to copy your accent perfectly, they will sound like they have an accent to native speakers who aren't from your country. So just tell them up-front that they are learning British English (or whatever dialect). Your students may not be happy to hear this, but at least they won't go through the entire class with impossible expectations for themselves (and you).

On the plus side, I think native speakers can be a bit more forgiving of English spoken with a fairly clear accent of another English-speaking country than they are of an imperfect attempt at their own accent. So this could work for them.

I've had this exact experience teaching students abroad myself. In almost all (if not all) countries, there will be regional variations in accent in the native language.

China is no exception. The easiest way would be to point out those parallels. Possibly something like how a Fujian accent is different from Guangzhou is different from Beijing.

You're right, in that when students are aware of such differences, they will have a sense of which one is "preferred," because that's also a fact of life in most countries. Probably in China the "Beijing standard" is the prestige accent.

For language teachers abroad, it's usually helpful to not have a strong accent of any sort. For Americans, that means a Midwestern style of speech. For Britons, BBC standard.