I complained an awful lot about the meaninglessness of grades when I was a student. But when I taught I found out how ridiculous they really are. The bottom line is really that teachers are forced to reduce an entire semester or year's worth of interaction and work to one rating. Which isn't entirely devoid of utility. But when you consider all of the rules, regulations, semantics, and politics that go into grading, then the utility dwindles pretty close to zero.
When I was teaching, students were given number grades. Teachers could give students any of the following grades: 50, 55, 65, 70, 75, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100. Grades below 50 weren't allowed b/c it would make it too hard for a student to pass for the year if they had a grade below 50 one quarter. 60 wasn't allowed because that was the pass/fail cutoff and they didn't want ambiguity. I have no idea why intervals of 5 were used below 90 and intervals of 1 were used above.
Maybe somebody from NYC was hired by Pittsburgh, because they've adopted one of these rules -- except in a much more bureaucratic and absurd way. The minimum grade a student can receive on any assignment in Pittsburgh is now 50. I'm unclear as to whether a student is given a 50 on an assignment if they fail to complete it.
The motivation behind the policy is sound -- they want to prevent kids from losing hope and, simultaneously, have more kids passing. But, in my mind at least, such an inane rule simply proves that the system is ridiculous to begin with. I'll leave you with my favorite quote from the article:
"one teacher . . . already worries about how awkward it will look when a student correctly answers three of 10 questions on a math quiz -- and gets a 50 percent"