Over at Unqualified Offerings, Thoreau has a bit of a rant about what students perceive as grading on a “curve”:
Moreover, many students have only the foggiest idea of what a curve is. Many (though probably not all) of their high schools had fixed grading scales with fixed percentages for each letter grade. The A/A- range is 90% or above, or 85% or above, or whatever. The B+/B/B- range is whatever percentage range below that. And so forth. If we set the grade markers anywhere below the ranges they saw in high school, that constitutes “a curve” in their eyes. We could base those ranges on the class average, base them on our own expectations of what we want from them on the test, or base it on some calculation involving tonight’s Powerball drawing. If the ranges are below what they saw in high school, they call it a “curve.” Besides, I submit that it is impossible to interpret a percentage cutoff without knowing two other things: The difficulty of the questions, and the partial credit policy. Without that, I simply cannot say if a given percentage is a reasonable level for an A, B, or whatever.
This fits fairly well with my experience, though there’s another population of students who assign a mystical importance to the idea of the “curve,” as if it will magically transform B- grades into A grades because reasons. Actually, my experience is that it really doesn’t make that much difference, at least in the intro classes.
Several years ago, I had a student who was really upset about ending up with a B+ rather than an A-, and because he had been a hard worker without whining during the term, I went back over the grades multiple times. I also went around the department and consulted everybody as to what they do to set grades, and tried all the different algorithms that were described to me.
In the end, every single one of the grading methods I tried put him at a B+, just short of an A-. Fixed percentage cut-offs, fixing the class average at a B and scaling up and down as appropriate, graphing the total point scores and looking for natural break points, fixing the high and low ends, and spacing the rest of the class between them– all of those gave the same result, in the end.
This shouldn’t be terribly surprising– we have an idea of what we expect and what the students expect, after all, and pitch our assessments with that in mind. When making up test and homework questions, I shoot fr something where even the deeply confused students ought to get the first part right, while only the best students will get the last part right. That typically ends up with an average in the 80-ish range, and if you call that a “B,” most classes very naturally fall into a roughly normal distribution about that (to within our ability to resolve the distribution given the small numbers we work with, anyway). Sometimes we get a strongly bimodal distribution– all high 80s and low 70s– but not all that often.
As a general matter, whenever I teach the intro classes, the best students will end up with 90+% of the possible points, which sets the threshold for A grades, and most of the rest fall in the 80% kind of range. The exact details of the grade assignment don’t ene up mattering all that much, so I tend to default to fixed percentage ranges– 85% is a B, 95% an A, 75% a C– and use the graph-and-check-break-points method to look at the borderline cases.
This term, we made a more radical departure, using standards-based grading. We assessed students on specific skills we wanted them to acquire over the course of the term– “I can solve projectile motion problems,” “I have a qualitative understanding of angular momentum,” etc. Each standard got a grade of 0, 1, or 2, and we averaged all the scores then multiplied by two to map to a 4-point scale. And the end result? A grade distribution that was basically indistinguishable from the usual. The average may have been slightly higher than usual– between B and B+ instead of B- and B– but it shook out about the same as always.
So, in the end, I don’t think “curves” or the lack thereof are really that big a deal. It’s easy to get sucked into a spiral of angst over the choice of grading methods, but at least for intro classes in the sciences, with lots of relatively objective graded work, it doesn’t make all that much difference in the end.