What criteria (in light of the best practices or teaching experience) should one consider when deciding the passing percentage of the course? (By the passing percentage I mean the grade threshold below which the student will receive an F)
How should the threshold below which students get a failing grade depend qualitatively on these criteria?
My classes are typically curved to the median. To grade, I first set what I think should be the median grade, based on my assessment of the class as a whole. Then one half of a standard deviation away from the median is one half-letter grade (e.g. if the standard deviation is 10 raw points out of 100, then 5 points would move an A- to a B+).
Using this scale, an F is simply someone who is a certain number of standard deviations below the median.
Several points:
I usually set 50%. However, I think the value is not of particular importance whatsoever - the main points are: Communicate the rule to the students and ask appropriate questions.
I usually tell the students that I have a 50%-pass policy and that this is basically arbitrary (I could easily devise questions such that nobody can pass...). I think, the question on percentages and grades can only be discussed in view of the questions on the exam and of the stuff covered in the course.
I'm at a school with nonselective admissions, and my process works like this. I look at what students have done in the course in past semesters, and I decide subjectively that a student who got x% deserved to pass. Then I look at the social/economic/political environment I'm in, and I know that if I set the standard at x, there would be unacceptable consequences, such as all of my classes having zero enrollment in the future. Therefore I lower the value of the variable x to what I think will prevent all my classes from being canceled. If this guess turns out to be wrong, I continue adjusting it.
I've honestly never understood the letter system for scoring. Is not intuitive and is open to so many interpretations.
Once I had to use letters, and at least for the case of failing the student it was quite straight forward.
Tests, homework, and every piece of work was graded in a scale from 1 to 10, at the end I just did a weighted average for the different elements.
So I ended up with a number between 1 and 10, I consider someone who has passed the class as someone who has at least more of half of the knowledge imparted in the class, so that would be having more than a round 5.
So the threshold was set at 5.1, I would fail those that got less than 5.1 and just prorate the rest of the letter upwards.
