I took Princeton Review TWICE over the course of 7 months. My score on my first LSAT was only 2 points higher than diagnostic test I took on the first day of LSAT prep class. So after taking the class one time, my score went up by 2 points. I took the class again, and on the second LSAT, I got 2 points higher than the first one. So a total improvement of 4 points. Not bad for $1,200.00
My teacher was cool and offered private sessions, but with our busy schedules, it was tough to meet one on one.
My advice: take a practice LSAT all the way through. If you are unhappy with the result, take a class, but not an expensive one. They are pretty much all the same. If you think your score is OK to get into the schools you want, get a book with practice LSATs and do them. The best way to improve is to just keep taking practice tests under timed conditions. Princeton Review had a good book that broke down the sections of the LSAT; how to set up the logic games, how to efficiently complete the reading comprehension portion, how to handle the arguments section...I would recommend that book, or one like it.