There are a couple of other branches in this thread waiting for your followup for the last few hours, and you pick this one? I still want to know if you think that "proficiency in the subject matter" is defined as "ability to pass a standardized test."
You think neither I nor the entire education system over the last 150 years have ever considered the effect of the principal agent problem? I even said "we also have oversight programs in place, including the department head, principal, and local school board." I elsewhere also pointed out to you how test manufacturers stand to make a profit if they can convince people to buy their tests, curriculum, and text books. They most certainly have a bias.
Your comparison to unit tests is telling, in ways you didn't mean it to be. Every project I've worked on has a very different set of unit tests, with essentially nothing shared between the different test cases outside some common test infrastructure.
Even multiple people on the same project end up writing different sorts of unit tests for the same code base. I do more functional and coverage driven tests, a co-worker is a red-green-refactor TDD developer. This diversity of tests is probably better for the overall code base than if we all did the same thing.
You do realize that teachers almost certainly have studied assessment design as part of their coursework, while most developers have almost no formal training in test engineering or experience in, say, coverage analysis?
If the goal is to test the students, then the teacher can - like the developer with good test engineering skills - develop the appropriate tests for the given set of students and expected knowledge. Except the teacher's tests must also be engaging and authentic, while the computer doesn't care what it runs.
And yet you think that one single set of unit tests for, say, all 8th grade English teachers can be useful enough to judge a specific student's progress, or a specific teacher's skills? Where does that optimism of yours come from?
Measure your outputs, ideally with unit tests, manual testing and the like. Does your code do what it's supposed to?
Standardized tests are basically unit tests for teachers - they measure whether the teacher's outputs are capable of reading and writing.
...talk with the teachers.
http://en.wikipedia.org/wiki/Principal%E2%80%93agent_problem
Note that the test manufacturer has no such problem.