Honestly... it's probably too early for you to start considering the GMAT. Most MBA students (full time) have between 2-6 years of work experience after undergrad. In fact, it is highly recommended at almost every MBA program around that you should have atleast a year or two of work experience. Some schools don't even take people with no experience. So the fact of the matter is that you are too far out. If you already have companies interested in you, I would recommend working hard to get the best internships and best full time job after school that you possibly can. This job will play a large role in what kind of MBA program you can get into.
I wouldn't recommend taking the GMAT any time soon. Your GMAT score is only good for 5 years, and even after 2-3 years your score becomes stale. The test changes over time, and its hard to know if old scores are still good reflections of how you would have done on the test.
Although the GMAT might not be the right decision right now (unless you're truly trying to go to a bschool right out of undergrad) you are still VERY smart to be looking so early. This give you LOTS of time to learn about the schools, what they look for, and improve your application. There is much more to the application then just the GMAT. In fact, the GMAT only makes up a small portion of the application. There is: Application essays, extra curricular activities, leadership experiences, GPA, work experience, Resume, etc... So what you should be doing is looking to maximize every area of the application you possibly can. Now, once you get a year or two out from actually wanting to apply to Bschool, then I would work towards the GMAT. Spend your limited time, resources, and effort towards other areas now, so you will have a super strong application in the future.
Look around, learn, and good luck!
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