It's been traditional in teacher training in the past few decades to emphasise the importance of teachers 'grading' their language to the level of the class they're teaching - in other words, only using grammar and vocabulary that the class have 'learned', or 'met', or 'done'. This is obviously due to a concern that learners should be in a position to understand what their teacher says; it also fits with a more general recommendation that teachers should minimise the amount of talking they do, so as not to take up too much classroom time which could be used more valuably by the learners.If you wanted to restrict your classroom talk to what the class have come across already, it would in theory be a fairly simple matter to refer to the coursebook or syllabus, or your accumulated recollection of lessons so far, and construct a mental corpus of the language you could allow yourself to use. In practice, it's not so easy to know exactly what learners know, or what they will recognise in spoken form. Nor is it easy to actually restrict what you say when you're in the middle of a lesson and you've got dozens of other things to think about. If you say something like "Pass your book to the person on your right" in an elementary class, for instance, it may be that: Some members of the class understand perfectly.One learner recognises the word 'pass' but gets stuck on trying to remember what it means, and loses track of the rest of the instruction.Another one interprets the last word as 'write', and gets confused.Another one is still struggling to segment the stream of speech they've heard into identifiable words.And so on. Nevertheless, practising being absolutely clear and minimal is a useful discipline, for the times when you want to say something once, be understood instantly and move things along as efficiently as possible. Here are a couple of things that can help with this discipline: It would be absurd to try to script entire lessons - you can't predict what will happen even in the most controlled and tightly-planned lesson. But in some lessons there are things - instructions, explanations, announcements - which you know you'll need to deliver and which can be scripted. So write them down and ask yourself: Is this as short, simple and clear as it can be? If not, edit it until it is. And then practise saying it, in a voice that's loud and clear but not unnaturally over-articulated. Record yourself teaching. Listen to bits of lessons where you're talking to the class, and if there are moments where they didn't understand - or didn't understand quickly and easily - ask yourself why not. Perhaps you inadvertently used a phrase they don't know? Perhaps you spoke too fast, or unclearly? Perhaps an instruction you gave was linguistically simple but just too long? Perhaps you didn't make sure you had everybody's attention before you started speaking? If you carry out this kind of investigation on a regular basis you're likely to become more aware of doing these things as they happen, and better able to reformulate immediately.However, it probably isn't a good idea to try and restrict teacher talk to this extent all the time. After all, the teacher is the best speaker of English in the class (probably!) and can play a very important role in providing listening and conversation practice, and putting new language into circulation. Here are some examples of how these things can happen: In a beginner's class, you might think "I can't ask them 'Have you finished?', because they haven't done the present perfect." But as long as they know the word 'finish' (maybe as a noun in a sports context) it'll probably be quite easy for them to interpret 'Have you finished?' at the end of a small-group activity, especially because the 'have you' is phonetically non-prominent, and a listener's attention is drawn to 'finished'. You might even choose to give them some more exposure by moving round the room to differen