Really late but Kurt often talks about how he will immediately reject people who makes mistakes that should not be made by their year. He had ranted in class about how someone who wanted to join a yr 10 class had x²>1, which was right, but then gave an answer of x>±1 (cue a "Are you kidding??"™ from Kurt and a failed entrance exam). It is a good idea to study lots of algebra, trig and geometry before you take the exam and make sure that you do as much as you can.
I was able to get in first try, but I remember not being able to finish all of them and only doing about 60% of the test.
The entrance exams for yr 9 onwards are crazy though, so I suggest getting into Kurt in yr 7, yr 8 or early yr 9 (where you do the entrance exam late yr 8) before everything starts becoming too competitive