Check out this article. it basically list out the most commonly discussed issues with standardized testing.

http://www.fairtest.org/facts/whatwron.htm

Standardized exams are structured to test one's mental skills such as short term memory. So a lot of times, you will find a student who just take a vocab memory class, or a prep class a month or two before the exam and end up scoring higher on these standardized tests than another student, who academically has a much higher overall GPA.