The more I think about this, the weirder it is.
Most GCSEs don't even have coursework/NEA. Which subject(s) are you talking about?
Which exam board? If it's CAIE your school may well not be registered as a centre with them.
Why do you think your teacher should spend time understanding a different specification, teaching you different stuff to the rest of the class, getting his head round the marking criteria for the coursework, and all for results that won't even count for the school?