The problem is that both sides are referencing a research device (in the form of standardized tests) about which most people understand very little.
A standardized test is a way of reducing some current state of things to a set of numbers that can be compared and analyzed more easily than words. For example, all the scores from the first time a reading test is administered serve as a statistical approximation of the current state of that population. A few students will answer a single item correctly, a few more two items, and at the other end a few will have answered all the items correctly, and a few will have missed only one or two. Somewhere in the middle of the score range will be found the majority of students, which when viewed graphically represent a curve.
Within the resulting curve several things can then be understood, such as where each student falls in the overall mix, or how a population of students changes over time when the test (or a comparable test) is administered at a later date. The nice thing about such instruments is that they represent a relatively cheap, unobtrusive way for approximating some very complex things.
But a standardized test by design is limited to approximating an overall status quo, and then showing where students, schools, etc., fit in relation to the rest. When a researcher uses an instrument in that manner, the results can be deeply informative, and the proper use of such is (and should continue to be) invaluable. Note that I said "proper" use.
Consider what happens when the purpose changes from research (the only proper use) to accountability (which is nowhere to be found in the design parameters of such an instrument): you risk making an instrument designed to approximate the status quo the basis for teaching and instruction. Let me say that again in slightly different terms: a policy maker that places accountability of any type upon a standardized test score risks focusing teaching and learning in such a way that it risks repeating the untenable present which was the very thing the policy maker wanted to change in the first place! The irony of making a standardized test the primary agent of change is frankly laughable--fomenting change was never in its purpose or design.
Consider the implications from a teacher's perspective. If your instruction is based upon a test, which is an approximation of the status quo, no matter how hard you teach you will find very little opportunity to actually move the system, since the test isn't about what might someday be, but about what is! Thus the political gesture that was intended to change the status quo serves to reify it instead. This problem is confounded with one of the worst things to happen to the tests used for accountability purposes, which is the establishment of a passing score (ironically named, in many instances, "meeting" the standard). That cut score further defines success not at the highest, most aspirational level of content contained on the test, but somewhere in the middle. Thus a teacher is deemed to be successful when they have taught the vast majority of their students content that is somewhere in the midst of where students are currently performing. That hardly seems to me a worthwhile definition of success.
But the frustration continues. In order to build a standardized test that will perform as designed items may come from a set of standards, but the only ones that are included are those that have good discriminatory power. An item that all students answer correctly or incorrectly may tell a great deal about what was or was not taught or learned, but fails to help understand anything about differences in a population. An item that half the students will answer correctly (and, conversely, half incorrectly), provides just the sort of discriminatory power required for such tests, and when grouped together with other items that behave similarly help to parse students into piles. Those piles, as was mentioned, go from those that answered no items correctly all the way up to those that answered them all correctly. Items that all students answered correctly or incorrectly don't contribute to that parsing and are eliminated.
A curriculum based on test items that were picked because they have good discriminatory power, and a curriculum based on what and how students learn will not and should not resemble one another. In fact, if the test serves as the basis for the curriculum--which it does in so many of our states at present--no matter how hard a teacher teaches or how much effort struggling students put into their studies, they will focus on all the wrong things and success will continue to elude them.
All because policy makers failed to ask basic questions about the nature of the key instrument they selected for determining success. They have, in effect, placed the present state of things as the definition of future success and now pretend to something else entirely--that high standards are just around the corner if only teachers would just do their jobs.
Which brings to my final point--the argument that if the test are so basic then students ought to at least be able to perform on that content and failure must be the result of poor teaching. The fallacy here goes back to the design. A standardized test is designed to parse students, not answer questions about what was taught or learned. Any assumption that a standardized test can be used to make such inferences requires a standardized test score to transmogrify into something that was never a part of the design. A standardized test score can certainly be used to show where a student or school ranks among others, but it is absolutely silent as to the cause behind that ranking.
As long as standardized testing remains the basis for school and teacher accountability, the successful schools we want for our students will continue to elude us, no matter how much effort we put into solutions. Teachers in Chicago--if they are like teachers in so many other places--are sick of looking like apologists for saying that standardized test scores shouldn't be a part of their evaluations, while fully accepting the idea of teacher accountability. Policy makers are genuinely concerned that schools don't seem to be getting better. Tools exist that were designed to accomplish what each side desires. Its time opted for them and acknowledged that the current tool isn't up to the task.