One must understand the potential benefits of standardized tests, of which there are many. First, standardized tests can be used effectively in the formation of summative assessments that can potentially be used as a guide to determine how much information a student has retained (note: this does not prove, necessarily, what they have understood). To this end summative assessments and standardized testing can also be used to uncover flaws in the curriculum itself (a technique I employ frequently). If 80% of the students of a given class miss the exact same question on the test there are only two logical possibilities; the question is poorly written and confusing, or the information pertaining to that question was not effectively delivered. Standardized testing can also be used in a secondary capacity to measure the teaching ability of a teacher; all things being equal (classes made up of the same demographic, teachers with access to the same curriculum and same resources), then the scores of multiple classes should be within a few points of each other, in theory. Any deviation above or below the median scores by a significant amount would warrant a closer look to determine what's going on.
The biggest problem that I have, personally, with standardized testing is that they are over-hyped and over-emphasized by morons in politics. Bean counters in Washington and at the State and County levels wanted a way that they could easily track and compare data about how much a student has learned and make a determination if a school is being "effective" or not, which in turn directly affects the decision of how much money the school receives. Reading essay questions would take too much time and be impractical, so they forced the standardized testing down the school system's collective throat. People who have little to no background in education are dictating policy on how the education system should be run; a recipe for disaster. Now they are even beginning to tie teachers' annual pay raises (and even their continued employment) to how well their classes do on these tests! Is it any wonder that 50% of all new teachers quit within the first 5 years and that education is quickly becoming one of the professions with the highest turnover rates?
I say that I've seen what's going on first-hand because I have experienced it in other areas. In the IT Industry, which I have worked professionally for many years, the certification that everyone wants/needs is called the "A+ Cert". It is a standardized test consisting of about 120 questions. There are literally "boot camps" that you can attend for a nominal fee they will cram the test answers in your head through rote memorization long enough for you to pass the test. Hooray! Now you have your A+ certification on paper, but you quickly forget the material for the questions, and worse yet, you have no idea what any of it means. You know that the answer to question 27 is B, but you have no idea why the answer is B. Under those conditions, is that certification actually even worth the paper that it is printed on? I don't think so. But, that's all that matters to the companies who seek out such candidates. Our school systems are quickly emulating these behavior patterns with more and more teachers "teaching to the test" because they, and their districts, have a vested financial interest in how well the students do on them.
Because the very system that we use to measure our students is flawed, every decision that is based on that information is also flawed as a result. Our school systems are performing poorly you say? Well, let's just throw more money at the problem blindly, because clearly if we just push enough money at the problem it will simply go away. Yet, annual studies by the US Department of Education comparing students from the G8 countries of the same age and grade reveal that while the US has the single most expensive primary and secondary education system in the entire world, our test scores and student performance is only middle-of-the-pack. Other countries are performing better with less money. Clearly, a change in our methodology is required to bring about effective changes in our scores. In that regard, I propose that teaching is just as much an art form as it is a science. In much the same way that you could not adequately measure the ability of a painter with a standardized test, it should not be the end-all, be-all of educational measurements either. Which would you rather have; the caricature painter at the fair who can crack out 100 paintings in a day, or Leonardo DaVinci who only paints 1 painting in a week? The quality of the student's cognition should be of paramount importance, more so than the quantity of their recollection. I would rather see students who are taught how to think, to reason, to research, to experiment and explore rather than to see students blindly parrot back the same information that I told them verbatim, devoid of intellect, curiosity, or desire to learn.