Ummmmm if your teacher is the fucked up type of teacher who doesn't know shit and just keeps telling you it's bad because she doesn't have anything else to say...kick her ass and never talk to her again. But as much as people like to say to each other "Even if it's absolute shit, just keep on writing!", i would just like to point out that sometimes...when something's absolute shit, even if you keep on writing...it'll just build up into a bigger pile of shit. The key is to really know whether your concept will work or not. So talk to a couple of teachers, talk to friends, talk to even teachers from other faculties. Ring up HSC helplines and ask those people. Just get some opinions on whether your work will work or not. IF most people says its good, and only a few says its not good, then you should just keep writing and any shitty parts will eventually be gone. If most people says its not going to work, i would strongly suggest you revise your idea and how you plan to communicate it.
Personally, my teacher is excellent. She's very encouraging and she definitely wants us to keep writing, and when we have something more complete, she can go through with us and pick out the crap parts.
But she has also made it very clear that if it won't work...she will tell us so very bluntly and we must listen to her advice because she knows what she's on about...being senior marker and all. So while your bastard of a teacher may not be the best source of advice, i wouldn't just discount EVERYTHING he says. Let's all remember. Praise doesn't get us anywhere. Criticism is what makes our works better.