Preparation courses mean nothing... It has been proven time and time again that its a waste of money.
When you do the past papers you are really only learning the format of the exam, and with section 3, the types of patterns that may arise... Also in section one, you learn the sort of questions they ask to distinguish between causation/correlation. You only need to do the three ACER booklets, and then understand where you went wrong. Perhaps look up a few words and thats it.
Of course the first time you do the exam you will get things wrong. Its only natural. ACER tests are different to anything you have done before. Learn the format, and your ready for any thing they may ask you.
I lol at idiots who pay some indians to try and teach them pure and simple logic...
ps. lol and in regards to STAT, my sister took the exam twice (as its run twice a year). Neither time did she have any preparation (besides the 2 booklets you buy)... The first time, she did it with a good nights sleep, food in her stomach etc.. and went well, but nothing special.
The second time she did it after a late night out, was hung over... she got the 3rd highest mark overall, and was pretty much accepted to usyd vet purely on that mark.
Think that speaks for itself.