Hi fstep,
At Kaplan we generally try to avoid making promises about numbers--someone starting from a 400 has very different prospects from someone starting at 600, and someone who took algebra three years ago will have a very different learning experience from someone who last took it thirty years ago.
However, at Kaplan we guarantee all of our classes. Students who aren't satisfied with their scores--even if they get a 790, and really want that 800!--can study with us again free of charge. Similarly, students who aren't ready to take the test can study with us again free of charge, whether they don't feel ready due to personal issues, low CAT scores, or simply sheer nervousness. Finally, any students who take one of our classes and don't beat their diagnostic score (or previous real GMAT score) can choose either to study with us again or to get their money back.