Grading on a Curve

A recent comment brought up the traditional criticism of grading on curves — what if 80% of a particular class did really well, and deserves As? what if 80% did badly, and deserves Fs? why not grade objectively rather than comparatively? — so I thought I’d repost my paean to curves from several years ago.(Note that this discussion is about curves in large classes, of about 30 students or more; for smaller classes, such as 12-student seminars, the curve is not apt, though of course there’s some controversy about where the cutoff size should be.

Lots of people really oppose curves. Shouldn’t people be graded on their own merits, they reason, rather than based on how other students have done? After all, they ask me, don’t you know the difference between an A exam and a C exam?

Well, yes, I do — but I can’t tell, just by looking at the exams, where to draw the line between an A- exam and a B+ exam. And this ties in to some of the reasons why grading on a curve is the lesser of evils:

  1. Sometimes I draft a hard exam and sometimes an easy one. I often can’t tell which is which, since they’re all easy to me — I know the material, after all! So something might look to me like a C exam rather than a B- exam not because this student is unusually bad, but because the exam was just harder than ones from previous years.
  2. Even setting the previous factor aside, I’ve been in teaching for 17 years now — but many professors are new, and don’t even have the data points that I have. In some areas, such as legal writing, the typical teacher has even less experience. (Likewise, in undergraduate institutions, many classes are traditionally taught by relatively inexperienced teachers.) Where are they going to get the distinction between A-s and B+s?
  3. Perhaps the curve is unfair to a class that consists of unusually strong students — but the absence of a curve is unfair to a class that has an unusually harsh professor. And the variation in class strength, especially classes of 50-100 students (the size of nearly all my non-seminar classes), is likely to be much less than variation in professor harshness.
  4. The pressures for grade inflation are quite real, and flow from basic human nature: Most people don’t like giving students low grades, especially once they’ve spent many hours with them. When I have small classes that can’t be curved as easily (since there are so few data points that there’s a higher chance that the class is unusually strong or weak), I feel this pressure myself, even if the class is still blind-graded. And of course if a professor is known for resisting this pressure, then fewer and fewer students will end up taking his class.
  5. Some people argue that the curve makes things harder for students to get jobs, but I don’t think that’s right. To be sure, a curve that’s harder than the curve at other comparable schools might make things harder for students, since employers might erroneously think that someone with a B+ average at school 1 has done worse than someone with an A- average at school 2, even if both grades are (say) at the 70th percentile in each school, and the difference is just a result of different curves. But that’s a reason to deliberately align the curves with your competitors, which in my experience law schools tend to do, not to abolish the curve (which could likewise lead to differences in median among schools because of differences in grading cultures). Indeed, a curve makes it easier to make sure that the median grade at your school is comparable to the median grade at competitors schools.

Of course, there may also be tweaks to the curve that might be worth doing in principle, like setting the norm for elective classes to be equal to the average GPA of the students in the class: This would take into account classes that attract unusually strong students or unusually weak students, and it would work because schools generally don’t have classes in their first semester of law school. But this is a small change on the margins, which might or might not be worthwhile in practice.

There are, I’m sure, many more advantages to the curve; and I think these advantages vastly outweigh the disadvantages. Like democracy, grading on a curve may be the worst possible system — except for all the alternatives.

UPDATE: Just to be clear, by “curve” I mean a range of ways to assure a relatively consistent distribution of grades from class to class. One model, for instance, would be to have 20% Cs (or below), 60% Bs, and 20% As, with similar subdivisions within each grade (though perhaps with some flexibility, whether +/-3% on each category, or with grades of A+ and C- being entirely optional). Also, to my knowledge most top law schools don’t have any mandatory Ds or Fs; the mandatory distribution is just for the As and Bs, and the Ds or Fs (if the instructor chooses to give any) would come out of the C or C- allotment.