I sometimes get contacted by students who have taken GRE classes at San Diego State University, UCSD Extension, or The University of San Diego, or who've taken a GRE class at the San Diego branches of big companies such as Sherwood, Kaplan, The Princeton Review, or Manhattan Review. As you can imagine, if these students are still looking for help, many of them did not get much out of those GRE classes! I have a few thoughts about why:
Class size. At SDSU, GRE classes have up to 50 students! At USD's GRE classes, there are as many as 30 students, and at UCSD Extension, you might be in a class of up to 24. (In contrast, our max GRE class size is 12.) As you probably know from going to college, the more people who are in the class, the less interactive and engaging it tends to be.
The materials aren't always useful. For instance, SDSU's GRE classes use CliffsTestPrep GRE General Test®, which is one of the worst GRE books on the market. Published in 2011, it's now out-of-date, and many of the questions in the book bear little resemblance to real GRE questions. I can only assume the company who administers the classes (BTPS Testing) mandates the use of that book, since it publishes the book. Although all companies should use the official ETS books and tests, many don't, since they can make more money using their own materials.
Instructors are a blind item. It's often tough to figure out who is teaching the course and how experienced he or she is. I know from personal experience that companies like The Princeton Review and Kaplan sometimes spend as little as 16 hours training instructors before sending them out to teach! If a class is inexpensive, imagine how much the instructor gets paid... and who'd be willing to not get paid very much.
So why do people still take GRE classes taught by these schools and companies? Since students at SDSU, USD, and UCSD often go to GRE classes on campus for convenience, these schools don't have to offer a very competitive product. Companies like The Princeton Review and Kaplan have an advantage because their brand names are so recognizable and because they literally have millions of dollars to spend on marketing. But just check out these schools and companies on Google and Yelp - their GRE class reviews are usually... not great.
Also, most people preparing for the GRE only end up thinking about GRE prep for a few months, max. They usually realize they need to take the test, do a little research, pick what looks like a good solution, and follow it. However, their ignorance (no offense) of the test prep industry often leads them to pick the easy, flashy, or convenient looking answer. Good test prep is hard work, and is not usually easy, convenient, or flashy... when it's done right.
Since companies often don't tell you who's teaching their GRE classes other than describing teachers as "expert instructors" or "leading experts in the field of test preparation", your guess is as good as mine about whether the instructor of the class will be a skilled teacher.
If their teachers really were GRE experts, wouldn't companies provide their biographical information or at least tell you their names? There are definitely some good teachers out there, but it may be tough for you to tell if the person teaching your class at a large institution is one of them.
If you actually can find out who's teaching a certain GRE class, do a little Googling. You want to know how long they've been teaching the material. Look them up on LinkedIn, and see how much of their career has been spent in test prep. But if you can't find out, I think the best way to take an educated guess who the typical GRE instructor is at a big company or college is to consider...
Let's think about the economics of a typical GRE class. Most companies pay instructors a set hourly rate no matter how many students take the class (and since big organizations often sign up as many people as possible, class sizes can be quite large). The company or school keeps two-thirds or even three-quarters of the course cost! (Most companies that offer GRE classes in San Diego offer GRE classes in every major city in the U.S. - they're focused on quantity, not necessarily quantity.)
If these GRE teachers were really "leading experts", why the hell would they be teaching a class in which the school or company keeps most of what students pay? What usually happens, in my experience, is that companies and schools hire younger, less experienced teachers who are content to make $20 or maybe $30 per hour. Tutoring is typically a temporary job for these instructors while they complete a graduate degree, or while they look for a "normal" job in their field.
A good rule of thumb is that if your instructor looks like he's 22, he really is 22, and he is not a "leading expert".
If big companies' tutors stay in the test prep field, they realize (like I did many years ago) that they can make much more working for themselves, they leave, and the company hires new people. This is another reason most companies don't tell you who is teaching their GRE course.
TL;DR: The GRE teachers at most companies and schools are not always, but often, underqualified, underpaid, and have to teach huge classes... simply because the companies and schools are trying to maximize profit and minimize their expenses. Maybe that's a good business model, but I don't think it is likely to produce the most helpful GRE class in the world.
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