I took some teacher training classes at Kaplan for about a month, intending to be a GRE and LSAT instructor. I never taught a class there since I got a much better-paying job, but the experience was interesting. I'm not convinced it's worth anyone's while to pay the rather exorbitant fees for Kaplan's services, so I'll highlight some good things and bad things about Kaplan (which for informational purposes is a subsidiary company of the Washington Post).
One thing I didn't like about Kaplan was the intent focus on appearances. Training was focused on making students feel happy with Kaplan, not necessarily on providing great instruction that would increase test scores. For example, I was taught that if I didn't know the answer to a question, I should pretend I did know and say something like "Aha, we'll be coming to that later." I was taught, and I was graded on my ability, to continually use words and phrases such as Kaplan, "Kaplan's proven test method," and "higher score on test day." My general impression was that it was much more important to convince students that Kaplan was helping them than it was to help them.
One good thing about Kaplan is they have tons of real tests from prior years. They have dozens of old LSAT's, for example. I am virtually certain that the best way to prepare for standardized tests like the LSAT is practice, so those tests are definitely useful. But keep in mind you can go to the bookstore and find dozens of old LSAT's and other tests. For my LSAT preparation, i went to Borders, sat in their cafe, and worked through a book of 10 previous LSAT's. Unless you intend to take significantly more practice tests, Kaplan's tests aren't that valuable.
But really, I simply don't agree with or find valuable many of Kaplan's test-taking strategies. For example, I would have been forced to teach students to explicitly write on their test booklets outlines, topics, purposes, scopes, etc. for every reading comprehension question they came across. I think it's inane to waste time considering and writing down your perceived purpose for a passage. And frankly, I found all of Kaplan's strategies patently obvious or superficial.
Kaplan documents the fact that students perform better after their courses. But OF COURSE they do. Typically students come in with no practice and no exposure to their tests. Then they take a bunch of practice tests and figure out what they're doing. My belief is that the best way to study for these admissions tests is to practice by yourself. I personally think the Kaplan courses are for people who want to be spoonfed because they want to avoid working test after test to improve their scores.