This is always worth looking at if you work in English language teaching or ELT as it's often referred to. The field seems to attract so many acronyms TEFL, TESOL, DELTA etc etc. Here's a sample from his A to Z of ELT which he seems to be compiling at the moment.
17 07 2011 
“O, swear not by the moon, the inconstant moon,
That monthly changes in her circled orb,
Lest that thy love prove likewise variable.”
(Romeo & Juliet)
"I have Shakespeare on the brain at the moment, having splashed out on tickets for three of the five shows that the Royal Shakespeare Company is putting on in New York this summer.
And, just by chance, I came across a fascinating book on Shakespeare’s grammar, first published in 1870, which details not only the differences between Elizabethan and modern grammar, but also documents – even celebrates – the enormous variability in the former. As the author, E.A. Abbott notes, in Elizabethan English, at least on a superficial view, “any irregularities whatever, whether in the formation of words or in the combination of words into sentences, are allowable” (Abbott, 1870, 1966, p. 5).
He proceeds to itemise some of the inconsistencies of Shakespeare’s grammar: “Every variety of apparent grammatical inaccuracy meets us. He for him, him for he; spoke and took, for spoken and taken; plural nominatives with singular verbs; relatives omitted where they are now considered necessary; … double negatives; double comparatives (‘more better,’ &c.) and superlatives; … and lastly, some verbs apparently with two nominatives, and others without any nominative at all” (p. 6).
As examples of how this variability manifests itself even within the same sentence, consider the following:
None are so surely caught when they are catch’d (Love‘s Labour Lost)
Where is thy husband now? Where be thy brothers? Where are thy children? (Richard III)
If thou beest not immortal, look about you (Julius Caesar)
I never loved you much; but I ha’ prais’d ye (Anthony and Cleopatra)
Makes both my body pine and soul to languish (Pericles)
Is there not wars? Is there not employment? (2 Henry IV)
Part of the RSC's summer season in NYC
Countess. Do you love my son?
Helena. Your pardon, noble mistress!
Countess. Love you my son?
Helena. Do not you love him, madam?
(All’s Well That Ends Well)
Elizabethan English was clearly in a state of flux, but is English any less variable now than it was in Shakespeare’s time, I wonder? Think of the way adjective + -er comparatives are yielding to more + adjective forms (see this comment on a previous post), or of the way past conditionals are mutating (which I wrote about here), or of the way I’m loving it is just the tip of an iceberg whereby stative verbs are becoming dynamic (mentioned in passing here). Think of the way the present perfect/past simple distinction has become elided in some registers of American English (Did you have breakfast yet?) or how like has become an all-purpose quotative (He’s like ‘Who, me?’) or how going forward has become a marker of futurity.
That variation is a fact of linguistic life has long been recognised by sociolinguists. As William Labov wrote, as long ago as 1969:
“One of the fundamental principles of sociolinguistic investigation might simply be stated as There are no single-style speakers. By this we mean that every speaker will show some variation in phonological and syntactic rules according to the immediate context in which he is speaking” (1969, 2003, p. 234).
More recently, as seen through the lens of complex systems theory, all language use – whether the language of a social group or the language of an individual – is subject to constant variation. “A language is not a fixed system. It varies in usage over speakers, places, and time” (Ellis, 2009, p. 139). Shakespeare’s language was probably no more nor less variable than that of an English speaker today. As Diane Larsen-Freeman (2010, p. 53) puts it: “From a Complexity Theory perspective, flux is an integral part of any system. It is not as though there was some uniform norm from which individuals deviate. Variability stems from the ongoing self-organization of systems of activity”. In other words, variability, both at the level of the social group or at the level of the individual, is not ‘noise’ or ‘error’, but is in integral part of the system as it evolves and adapts.
If language is in a constant state of flux, and if there is no such thing as ‘deviation from the norm’ – that is to say, if there is no error, as traditionally conceived – where does that leave us, as course designers, language teachers, and language testers? Put another way, how do we align the inherent variability of the learner’s emergent system with the inherent variability of the way that the language is being used by its speakers? If language is like “the inconstant moon/that monthly changes in her circled orb”, how do we get the measure of it?"
In attempting to provide a direction, Larsen-Freeman (2010, p. 53) is instructive:
“We need to take into account learners’ histories, orientations and intentions, thoughts and feelings. We need to consider the tasks that learners perform and to consider each performance anew — stable and predictable in part, but at the same time, variable, flexible, and dynamically adapted to fit the changing situation. Learners actively transform their linguistic world; they do not just conform to it”.
References:
Abbot, E.A. 1870.
A Shakespearean Grammar: An attempt to illustrate some of the differences between Elizabethan and Modern English. London: Macmillan, re-published in 1966 by Dover Publications, New York.
Ellis, N. 2009. ‘Optimizing the input: frequency and sampling in usage-based and form-focused learning.’ In Long, M. & Doughty, C. (eds.)
The Handbook of Language Teaching. Oxford: Wiley-Blackwell.
Labov, W. 1969. ‘Some sociolinguistic principles’. Reprinted in Paulston, C.B., & Tucker, G.R. (eds.) (2003)
Sociolinguistics: The Essential Readings. Oxford: Blackwell.
Larsen-Freeman, D. 2010. ‘The dynamic co-adaptation of cognitive and social views: A Complexity Theory perspective’. In Batstone, R. (ed.)
Sociocognitive Perspectives on Language Use and Language Learning. Oxford: Oxford University Press.
To see the original article, here's the link:
http://scottthornbury.wordpress.com/2011/07/17/v-is-for-variability/
Ofqual, the exams regulator of the UK government, has confirmed that Cambridge ESOL's Delta qualification for teachers is at the same level as a Master's degree or a professional diploma in the European Union. This is a result of Delta being placed at level 7 of the UK government’s Qualification and Credit Framework (QCF), making it the only English language teaching diploma currently included at this level. 
