The factors that make standardized tests inaccurate are called "test pollution." There are many factors, which leads to the questions, exactly how accurate are these things and why are we spending so many educational dollars on something that is probably wildly inaccurate?

Psychological pressure seems to be a huge factor in "test pollution." Here are some examples.

Reynoldsburg article (local example). A teacher's evaluation is based in part on her students' improvement (as defined by tests). It's no wonder that a teacher might want students to do badly on the initial test at the beginning of the year.

Here is an excerpt from a book that shows how the pressure on those who score the tests can also add inaccuracy. Toward the end of this excerpt is where the particular practices that lead to inaccuracy are highlighted (if you want to skip some of the descriptions of how tedious the work was and the personal characteristics of those who did the work):