Okay, so what makes a “good grade”?

At my institution of higher learning, an A+ translates into a 4.33 (4-point grade scale), an A into a 4, and so on. Big deal; there’s a standard mapping of letter grades into four-point grades, which makes it easy for anyone to evaluate one grade in the context of another.

But what about mapping marks (“You got a 74% on the third assignment”) into grades (“You got a B- in Intro Computer Graphics”)? How does the one get transformed into the other?

My favourite answer is “it depends”. Marks — at least in theory — are entirely empirical things. You get so many marks for satisfying each part of the assignment specification. If you implement this and this and this, you get this many marks. Sure, fine. That’s fairly obvious.

But when you take those “earned marks” and translate them into “overall grades”, you need to mess with things a little. Maybe my section of CMPUT 321 is tougher than Dr. Choad’s section of CMPUT 321, because I asked my students to write a Monte Carlo raytracer for their second project and Dr. Choad asked them to write “Hello, world!” in OpenGL. A 40% in my section is worth an 85% in his section, but they both correspond to an A-.

Or do they? How can you tell these things until the end of the semester?

My undergrad education was full of these problems. One prof of mine — intro deductive logic — complained that he’d promised everyone with a 90% or better average a 9 (on a 9-point scale — no, not a stanine), and a third of the class earned 90s. (That class was amusingly bimodal: most of the Arts majors who figured that a Philosophy course would be easier than a Math course failed it, and most of the CS majors who figured that a Philosophy course on logic they’d taught themselves in the eighth grade would be easy meat aced it. But I digress.) Another prof of mine thought it’d be reasonable to expect a 50% or better average from students, and that he could fail the rest — but he’d never taught an undergraduate analysis course before, and after the midterm the class average was 44%.

Several friends of mine took honours-programme math courses, in which a 40% was often the best mark in the class. They were crushed until they realized what was going on — they weren’t expected to understand everything perfectly, just to get the gist of what was being taught. On the other hand, I can’t really bring myself to believe that it’s okay for students to earn less than half of the available marks on a given assignment — what’s the point?

Back to the first question, then: what makes a good grade?