Do-it-yourself is still the way most people study for the exam. Forming a study group will likely be better than going it completely alone, but the simple fact is that you could study on your own or with peers for months and still not be able to identify a majority of the subtle tricks and traps that can confound you on test day. Only professional preparation can give you the inside track to this tricky test, and 1-on-1 tuition is the most effective form of test preparation available.

Given that... 

• the GMAT is effectively the door-opener to business school, 
• the return-on-investment (i.e., subsequent career and earnings growth) from top business schools far outweighs that from lesser ones, and exceeds by a factor of 10-100x even the most expensive investment in improving your score, 
• people almost always do better with high quality help than they do without it 

...shouldn't the only question be: how can I get very best help that money can buy? You're about to make a huge investment in a business school education; taking out a little insurance to ensure that investment pays off handsomely is simply good risk management.