tkherrmann wrote: Also, I've heard LOTS of people say that test prep companies skew their score reports low so that when test day arrives, your resulting score makes it look like the company helped you improve. Of course, this effect probably varies from company to company.

It certainly varies from company to company, but there are a few reasons why companies have a commercial interest in producing test scores which are too low:

-if you get an 800 on their test, you're not going to think you need help, so you won't buy anything from them;

-if the company offers some kind of guarantee ('you'll improve by 150 points!') and that guarantee is based on a comparison between a score on a company test and your score on the real test, the company has a clear incentive to produce low scores on their test, so that they will not need to honor that guarantee as often.

Even companies which make an honest effort to produce reliable scores - and some do, certainly - run up against the difficulties of emulating the GMAT scoring algorithm. To do this well, you need to compile a lot of data on each test question, and only GMAC has a large enough test taking audience to do this successfully.