However, there are so many ways that standardized tests fail to properly measure a student's level of achievement. I have seen great students perform poorly on tests which covered information that I know that the student knew well. Less frequently, I have seen poor students luck their way beyond their ability. More often, I have seen students blow off tests because they do not understand the value of them or are afraid what the test might say if they give it a true effort.
The tests are a period of stress and confusion. Not only does the testing time itself take away from instruction, but the aftermath of the tests can lead teachers to focus their efforts more on helping students navigate the tests rather than actually learn the material. There are methods to test-taking that can provide better results than actually learning the material … at least, for that particular test.
However, to circle back, without some level of standardized, unbiased testing, it is difficult to know what skills might need reinforcement. Having a baseline can also get teachers to have a common set of data on which to base their decisions rather than trying to feel their way to the problem. It can also be a way to demonstrate proficiency and even mastery so that the same educational path does not have to be tread time and time again.
I will say, though, that proctoring those tests is both mind-numbing and exhausting.