One of my high school English teachers liked to remind us students that he had more control over our grades than we did. We spent about 3/4 of one marking period working only on grammar and sentence diagramming, which most of the class learned well enough to get high scores on the quizzes and tests. After we finished our grammar section, I had a very high A average, as did most of my friends.
But I didn't get an A for the marking period. The teacher designed the grammar section to end with enough time left in the marking period for us to read and be tested on Death of a Salesman. The teacher himself called the test "the death test" and bragged that nobody ever got an A on it. The goal of the test was to pull down our grades and reduce the number of A's given out that marking period. I scored in the low 50s on the test and, as a result, got a B on my report card, in spite of the fact that I'd gotten a high A on everything except that one test. The same thing happened to a bunch of my classmates, too.
Imagine if my teacher had been required to give not grades but a specific evaluation of what we'd learned that marking period. He would have to have admitted that I'd mastered the entire grammar curriculum and that I'd done poorly only on the literature test (which tested the singular skill of regurgitating, word for word, the teacher's interpretation of the play). Such a system would have completely emasculated this guy's power play with our grades.
Most people who've been through traditional schooling can tell at least one bad story about grades. It's just one of those unfortunate school rites of passage. We all move on and realize that one bad experience won't affect much in the long run.
That said, it's refreshing to know that a school district near me is replacing the standard letter grading system with a more comprehensive skills evaluation system. The system, based on the state standards for each grade level, lists all the skills covered in each curriculum area and denotes where each student stands in relation to the standard: beginning, developing, competent, excelling.