The process of deciding which instructors are assigned to which course offerings is a complicated and somewhat messy one. It starts with a form that professors and lecturers fill out every year or two, listing the courses they wish to teach. Their expressed wishes are the dominant factor in course assignments, since there does not exist any mechanism to force someone to teach a course they do not wish to teach (and even if there were, their students would probably be the ones that suffered).
The form asks in which of the three terms in a year the instructor wishes to teach, and asks which courses they wish to be assigned. It used to request that at least one nonmajor course and at least one course in first or second year be chosen, but this was widely ignored, so it no longer asks that.
I try to put down four or five choices for each of fall and winter. I don't teach in the spring term because that's when my kids have vacation, so that's when we can get away. (Technically, I have five weeks of vacation, but it is almost impossible to draw a line between work and play for me; I nearly always have some work close at hand, as well as a computer.) Since most institutions don't have a spring term, it is a traditional time for research; many conferences and workshops are scheduled, and colleagues are more free to travel and visit for collaborations.
The contents of the forms are known only to those who do the course assignments, but I get the sense that many professors list one or two courses in the core plus fourth year courses in their research area. The form also asks us about graduate courses, which tend to be more rewarding to teach: the material is more advanced, there are a smaller number of students, and it is a way of attracting graduate students to work with. A first-year undergraduate course can't really compete with that.
I also have the sense that there are professors who only list one or two courses in total -- and that they more or less get their way. As I mentioned above, there is no real way to force them to do otherwise. Tenured professors can lose their job only by not showing up to teach or for severe breaches of ethical guidelines.
The flip side, of course, is that there are certain people that you don't want teaching certain courses, even if they are willing. There are also not enough teaching tasks among professors, lecturers, and academic staff to cover all offerings necessary to meet promises made in the calendar and to keep class sizes at a reasonable level. So some fraction of offerings each year are taught by sessionals -- people hired on a term-by-term basis. Some of these people make a shaky career out of whatever the School can offer them; some are graduate students getting some useful teaching experience; and some are "warm bodies", hired because the alternative is to endanger graduation dates by cancelling sections of core courses.
So someone has to take the preference information, plus whatever they can glean about who teaches what course well and who would be a disaster, and come up with an assignment. This is of necessity an art, not a science. The preference forms also ask about desired teaching slots. Some people like to teach at 8:30, but most don't. The Tuesday/Thursday 80-minute morning and afternoon slots are in high demand, but there are only so many courses that can be scheduled there.
The university moved in recent years (a decision taken somewhere in the Registrar's office) to a sort of fixed scheduling system, in which a course offering in a given term is at the same time as it was in the previous year. A given instructor's course and timing preferences may be in conflict with this schedule, resulting in more friction.
It's no wonder, then, that the course assignments are a bit of a surprise when they come out in late winter or early spring, and that there is a period of shuffling around immediately following their distribution. I don't think the process is anything close to "fair" -- I'm not sure how one would define that -- but I've been reasonably happy with my assignments to date. --PR
(Adapted from a blog posting made June 26, 2003.)