My theory of how students make sense of professors: Whatever conception of "God" students bring with them to college gets applied to their male instructors. Whatever conception of "Mom" they bring with them to college gets applied to their female instructors. Students are, on the whole, more likely to accept that God will, on occasion, be angry, distant, vengeful, than that Mom will behave in these ways. A Mom who isn't unfailingly nurturing is a source of dismay. Any characteristics (race, ethnicity, gender ambiguity, relative youth, disability) that complicate students' ability to assimilate male instructors to God and female instructors to Mom is also a source of dismay. Over the course of a productive semester, good students will gradually break free of these preconceptions and come to engage with instructors in terms of their authority and knowledge. Getting to that point, however, involves working around these unspoken, unacknowledged assumptions.
So it should be no surprise that the conversation about what to call college instructors continues. Will Miller, responding in Inside Higher Ed to Katrina Gulliver's article on first names, says it shouldn't matter anyway: that an instructor should be able to convey authority independently of any form of address. (Response from the twittersphere: easy for a white male administrator to say!) Students are quicker to apply the "professor" label to some people than others, based predictably on gender, race, and age (not necessarily in that order). The more it stretches students' mental capacities to accord the instructor standing in front of them the same aura of authority that they would attribute to a tweedy, bearded man, the more crucial it is that they be asked to stretch in that way. But yes, not all instructors are created equal. Rebecca Shuman points out in Slate that college students are confused about who exactly is teaching them anyway, and with good reason: adjunctification has unsettled old categories, multiplied academic descriptors, and boiled away the jobs that used to be filled with the tweedy bearded types. Perhaps we worry so much about titles because we no longer know how to recognize the selves we were trained to be.