Thanks for writing in. Enrolling in additional coursework is a great way to address a deficiency in your GMAT score or undergraduate performance. I can't really comment on a certification program without knowing what type of program you're thinking about or what your background/goals are, but in terms of classes, you'll want to focus on coursework that is directly applicable to an MBA curriculum.
Common courses candidates take include Corporate Finance, Statistics and Accounting. You can use the optional essay to make sure the schools know you are taking these steps to enhance your candidacy.
Best of luck!
daniel at mbamission
Daniel Richards, Admissions Consultant
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