Every lesson at Dr Du, he will go through the easier ones first, then progress onto extremely hard ones. Since, some of the homework questions, easy and hard, are done in class, you will find hwk easier to do.
I had a family friend who went to James Ruse. During her prelims, she was like near the bottom (ranked 100+) of her cohort for English adv. She then managed to get above 90+ for English, with an ATAR of 98.95. I know this is only English, but thats the only story I can think off.