An MBA can end up costing as much as $100,000 in tuition-and that's not including the time lost that might be spent building your career outside of the classroom. Is they really worth that kind of investment?

In fact, when it comes to goosing up your lifetime income, an MBA just ain't what it used to be, according to Jeffrey Pfeffer of Stanford and Christina Fong of the University of Washington, writing in the journal of The Academy of Management Learning and Education.  They cite studies showing that while MBA grads earned higher starting salaries than non-MBA college grads, mid-career MBAs saw no salary boost after earning the degree-and that those who pursued an MBA full time suffered from the disruption in their employment.

Declining Payoff

"It's become unclear whether it makes sense to overburden yourself with expenses and loans in order to secure the possibility of a greater salary in the future," says Pfeffer.

Unfortunately, many people still enroll in MBA programs under the assumption that it will have a huge ROI, when that's simply not true, according Anna Ivey, a former dean of admissions at the University of Chicago. "If [an MBA] is something that you're doing because you want to make more money, rather than because you're really interested in how businesses function, you'll probably be disappointed," she says.

Studying the Wrong Subjects

Another problem with an MBA: The courses you take may be too theoretical to be of much practical use. Many MBA courses are based upon "best practices" and case studies, but few students (and even fewer professors) ask the obvious questions like: What in God's name does the success of IBM in the 1990s have to do with how to run a start-up today? Or why are we studying Apple and Coke, when those brands occupy exceptional, and probably not replicable, market positions?

Another reason that an MBA investment might prove unwise is that you'll end up taking courses in management theory, which is frankly a huge load of horse manure.  As former management consultant Matthew Stewart points out in "The Management Myth," management theory promotes both rationalist approaches (i.e., manage by the numbers) and humanist approaches (inspire, empower)-even though the two approaches result in diametrically different management behaviors.

The simple truth is that you can't teach management in a classroom, according to Henry Mintzberg, a professor of management studies at McGill University and author of "Managers Not MBAs," a groundbreaking critique of the business school curriculum. "The MBA trains the wrong people in the wrong ways with the wrong consequences," he says.

What About Sales?

Nowhere is the impracticality of MBA programs clearer than in the way they generally ignore sales-the single most important function of every business. Only a handful of business schools even offer courses on selling, let alone majors.

This is beginning to change.  As I explain in a special report I just wrote with Howard Stevens, CEO of Chally Worldwide, there is now a behind-the-scenes movement inside some top business schools to make MBA programs more practical by adding a sales component to the course mix.  However, such programs remain exceptions rather than the rule.

For the time being, you should probably look at that MBA program-and its shiny recruiting brochure-with fair amount of healthy skepticism.   It's not that you won't learn something, but if you sign up for an MBA program that's impractical, you may end up learning an important business lesson: that there's sucker born every minute.

If you found this post helpful, click one of the "like" buttons or sign up for the Sales Source "insider" newsletter.