English, like what most people said, is very subjective in terms of grading, and the fact that there's no distinct mark allocations means it becomes even more subjective when teachers rank students, despiting the fact that a large number of students may share similar writing standards. Your exams will be marked subjectively too, think about it, some examiners prefer certain colored pens to another, some examiners hate small handwriting and some hates double spacing, subjectivity is just like... the nature of this subject and due to the importance of English, I guess we just need to live with it.
From what I recall, SACs take up about 50% of your English SS. Although your cohort performance in the Exam can dominate whether your SAC component be scaled up or down, your ranks are still set. So, for English, SACs are indeed quite important comparing to other subjects' SACs, especially if you come from a weak cohort.
IMO, teachers can dislike certain students but when they allow this emotion to affect their markings too much and even attempt to hurt the students' self-esteem, he/she is simply unsuited to the job. For example, my ESL teacher ( A roughly 38 yr old boyfriendless fat women who said she hates everybody called James) would say "I can't stand Beijing Opera, its just the wieredest thing ever." in front of the whole class which included 10 Chinese students. How could somebody just discriminate another country's precious culture like that? I think she hated everybody in the class but sometimes she acts differently. One day she would ask me to go to the front to demonstrate an enthusiastic handshake with her to the class ( yeh.. a handshake -_- ) another day she would tell a girl to get a pass from the coordinator because of the extra shirt she wore underneath her uniform when the poor girl asked her to turn off the heater which was right infront of her. Once she even said she hates ambitious people who always try to go ahead of others, forgetting bout how she commented b4 on herself of being not ambitious enough at uni which caused her to teach now. And another teaher at our year level revealed to me that I got three 79s for my SACs, before that I was pissed till death because of the constant B+'s i was getting- we were only allowed to know our grades.. hmm so basically your teacher can do whatever she wants with your ranking/marks.
Guys, my one piece of advice being: Never ever argue with your teacher and you are free to bitch about him/her once year 12 finishes. =]