Objectivity is a unicorn. It's inspiring to believe in, pretty to create pictures of. Some folks love the idea of objectivity so much that they dress up horses or try their hand at photoshop. But at the end of the day, it doesn't actually exist.
Nevertheless, we continue to enshrine the idea of objectivity in places where it does not exist. Writers have repeatedly reminded us, for instance, that internet search engines are not objective. This article from Michael Kassner at Tech Republic provides a good summary of the basic arguments. When you google something, you do not pull up some objective summary of what the internet contains, but a list that has been weighted by programmers who judge that certain factors should be considered (including a cyber-reading of you and your own proclivities). Google results are just as subjective as if they were compiled by some guy and his buddy making their best guess about what you want and what you should see.
But we really like to believe in Objective Facts, and in particular the notion that certain instruments provide such facts for us.
Some simple instruments do provide some rudimentary objective data. A measuring stick will provide an objective indication of length of an object. But the stick might be measuring meters or feet, and it might include hatchmarks for very small units or not, and if you're using to measure something that's not exactly straight, you will have to make a judgment about how do that. Even the simplest measurement includes subjective judgments. And that's working with objects, not humans.
Complex measures are mostly subjective judgments, whether we are measuring all the articles on the internet and how well they match your search terms, or we are measuring how "college and career ready" your eight year old child might be.
We keep talking about standardized tests as if they are objective measures of... well... anything. They are not. A standardized test is the product of the individual personal judgment of the test writers, who have their ideas about which specific bits of knowledge and skill should be tested and who make their own judgments about what exact tasks would measure those bits. They may claim that research backs up some of their choices, but research is itself the result of individual subjective judgments and choices made by the researchers deciding what to measure, how to measure it, and how to interpret the data they generate. In some cases, such ads David Coleman's reconfiguration of SAT vocabulary, they simply baldly say, "I think we should do this, not that."
Track the elements of standardized tests in any direction you wish; you will soon arrive at human beings making personal subjective judgments about how the test should work.
Reformsters keep talking about the use of testing and data as if it will result in replacing the varied subjective judgments of a teacher with the pure objective results of the testing. No such thing is true. What they seek to do (whether they understand it or not) is replace the judgment of the teacher in the classroom with the subjective judgment of the persons who make the test.
When someone claims "this test is an objective measure of a students language use ability," they are wrong. The test is, at best, a pretty good subjective measure of some tasks that some test-writer guys believe probably indicate language use skill. It is no different from having some person come into the classroom and say, "I'm going to sit and talk to Pat for a couple of hours, and then I'll tell you how good a reader I think he is."
It is not humanly possible to remove subjective judgment from education (or, arguably, anything at all, but let's narrow our focus for now). Never even mind the question of whether or not we should-- it cannot be done.
How do we deal with the inherent subjectivity?
The problem with subjectivity is that it solves problems within a personal framework. We operate in our own little bubble or silo and we define problems and search for solutions based on what we see and know inside that little framework. The trick is to temper subjectivity by expanding that framework. We need to see and know more.
We expand the framework with professional knowledge. We train teachers to understand pedagogy and subject matter so that their instructional judgment is not based on considerations like "What kind of mood am I in" or "Do I like this kid."
We expand the framework with personal relationships. One of the terrible lies of the cult of objectivity is that we can make good decisions about students without knowing a thing about them. Management schools recommend that managers not live in the same communities as their employees, so that relationships are not part of their framework.
Baloney. One of the marks of a good decision is that you can talk about it out loud with the people who are affected by it right there in the room with you. When our framework is expanded to include the people who are part of the choices and the results, our subjective view of the situation is more complete, more useful to people beyond ourselves.
Reformsters have done their damnedest to keep teachers, students, and much of accumulated wisdom of American public ed outside of their framework. This leads them to say naive things (Hey, did you guys know that water is wet) and stupid things (Hey, if you tried hard, I bet you could build a house out of water). It doesn't ever lead them to say objective things.
They claim that their goal is to inject objectivity into the education world, when in fact they're simply trying to impose their own subjective judgments in place of others'. When someone wearing a white hat rides into town on a unicorn, you'd better check to see how the horn is attached.