I have explained myself on this topic several times. I have created polls about it and I have expressed and argued my point of view many, many times. If you are curious of all the reasons why I support this testing, then please check out my debates and polls -
Kids do not learn at the same pace nor should they. Every kid is different, learns differently, and at a different speed. It is not also not a true reflection of knowledge. It's a reflection of how well a kid can memorize and regurgitate specific data at a specific time. I was a straight A student but never did well on tests because I found them boring. Also, a lot of kids feel pressure to perform at a certain level and cave to that pressure. I find that standardized tests are a waste of time and money.
Even my teachers and the faculty at my school do not support it because they know the information on the tests isn't presented realistically. One test shouldn't determine anything about your future, it puts an extremely amount of unnecessary pressure on students. They are outdated and worded in such a way that purposefully makes it more difficult than it has to be.