They shouldn't be doing it and if you have a complaint, speak to your year advisor. If it isnt resolved there, speak to the deputy principals and then the principal himself. If it still isn't resolved, speak to someone at the department of education - or get your parents to call on your behalf.
As i am doing an education degree, i do know that teachers are under no circumstances (regardless of what race they are or the race of the student in question... and even intelligence level, and in general a good worker) allowed to do what you have described.
Besdies, if your hsc marks are higher than the class marks, the Bos start asking questions about the teacher's competance and practices.
Anyways, i have a friend who was supposed to have her special provisions paperwork filled in and the principal wasn't doing his part. Her mother escalated it to the Department of Education, and it got as high up as the Minister for Education. The principal was put under an edict, which is where the Department sends people in to see if everything is being done correctly.
Good news: she got her special provisions and she sat for her HSC and is now at TAFE studying business.