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Some schools may also require you to take one or more GRE Subject Tests. The purpose of each GRE examination, of course, is to help graduate schools decide if you've got the right stuff for their program. If you're looking for help with the exam, check out Peterson's full-length GRE practice test.
Doing well on the GRE can require a good deal of preparation. Although the exam's designers say the it's intended to measure only general ability -- meaning you shouldn't have to study for it -- that doesn't mean it's a good idea to simply walk in on exam day and hope for the best.