I think it's a mixture of both. On my first lsat diag I scored in the 120s. On the actual test I scored 173. It really depends on the individual. I believe that if you work hard, anything is possible.
My first diag was so horrible because I had NO idea what to look for on the lsats. I was answering questions based on common sense, not logic. Then I started to learn more about the lsats and on my own I went up 30 pts. My biggest weakness was type 2 questions and the games. Once I learned how to do the games it was over. While I was doing testmasters, everyday I focused on mastering the material taught in the previous less. I really started. Needless to say I didn't have much of a social life those three/four months. Everyday i put in 2-3 hours of studying. Most people aren't willing to do that. Then I made flash cards for certain terms like suffiecent/necessary, logical opposites, rules for cause and effect, and negation techiques. Even after I understood the concepts, I would always review the information. On average I would spend 15-21 hours a week studying on topic of school work, intership and my other commitments. That's why I said if you are willing to put the work into the lsats, you can do very well.