To the OP:
I think that typically it's harder to make a big jump if you've already had significant exposure to the LSAT prior to taking a class. That being said, however, there are exceptions. My Powerscore teacher said that he had a student who had already taken Kaplan and then took his class and started out at a 161. She improved to a 176!
I had basically zero exposure to the LSAT prior to taking my Powerscore diagnostic, and I got a 163. I missed only 1 RC, 7 in the first LR section, 4 in the second LR section, and then 11 games questions (out of 24! pretty embarassing). My teacher said that he's optimistic for me because people tend to make the most improvement on the games sections. I'm hoping to get in the mid-high 170s.