Coming from the perspective of someone who tutors students in a variety of subjects, it is definitely the case that people will only get out of a tutorial what they put into it. One must realize that there is no such thing as a course that can guarantee you an improved grade, because it depends so much on what the individual contributes to their own studying.
And also, there are many factors which could adversely affect one's grade that are completely out of the control of Kaplan, such as physical health, bad proctoring, panic attacks, etc.
For the record, I'm not taking any course; I just bought several books to study from, because there's no way that I can afford $1000 for "any damn LSAT course"
And I really think that the strategies that you can learn from any course can also be learned from a book...