By Dick Tibbetts, University of Macau, China
If you are teaching spoken English then you should teach as it is spoken. There is a myth that formal English doesn't use contractions like 'it's'. This is just not true. Listen to anyone speaking formally, say in a presentation to an audience and you'll hear plenty of contractions. You'll hear slang and other items marked as informal too, but at a lower frequency than in everyday conversation. These items are there to empathise with the audience, while the formal items are used to give a sense of occasion. Overformality antagonises the listener. The use of full forms and non use of slang certainly doesn't show a better education.
By the way, there are many more contractions and elisions in connected speech than those marked by apostrophes in written english. As well as 'it's' and 'can't' there are things like I'd've for 'I would have', where the ' in d've indicates a schwa, a weak vowel sound like the sound between 'k' and 'n' in 'spoken'. These weak forms are vitally important in spoken English as without them you lose the stresses and rhythms of spoken English. Chinese learners tend to pronounce each syllable with equal stress and this makes them hard to listen to, a bit like listening to a machine gun in slow motion.
If you teach them to speak as you speak that's a step in the right direction but it might be an idea to leave a tape recorder on at breakfast time and at work for a week or two and try and analyse how you really do speak.
Here's an interesting story. Some 20 years ago in UK I had a Chinese student who insisted he did not need English because he was studying science and he had a basic grammatical knowledge and a command of technical vocabulary for his subject. He did not feel he had a need to speak or to indulge in social chit chat.
I overheard him once as he was carrying a load of books. He couldn't get into the classroom and he asked a fellow student, an Arab, "Can you apply a torque to the door".