[bzbarsky]

> Candidly, no one would pay for a prep course for a 30 point gain.

My understanding of the research in this area is that the 30 point gain is if you compare people who take a prep course to people who put in an equivalent amount of time preparing on their own with the widely available (e.g. can check them out of the local public library in many cases) preparation materials.

The 200 point gain is if you compare people who did the prep to people who have not done any prep.

The set of people who can't make themselves put in the time without the structure of a course would benefit by a lot more than 30 points from the course, and would pay for it. And do.