Hey RL,
I promise we're not just being cagey, but there's no answer to that. The reason why is this. The VAST majority of students don't let us know how they did on the actual test. Once they've taken the class...they're gone. Also, the ones who DO report tend to have done well (they're writing to thank us), so if we used that data, it would be pretty biased.
To make things even more complicated, a lot of students take the class but don't do any homework, or don't take any practice tests, so they're data would also be compromised.
To make things even MORE complicated, improvement is much easier the lower your starting point. So a student who starts with a 90th percentile score will struggle to improve to 95th percentile, while a student who starts at 20th percentile will almost certainly get above 50th percentile, even if they didn't work that hard.
So there's a long answer explaining why I can't give you an answer!
That said, the majority of people who do the work as we assign it see an amount of improvement that they are happy with. I can say that because after teaching for many years, I can count the number of people who've said "I did all the work but didn't improve" on one hand.
Hope that helps!
-t