Teaching where I do (not just this college, but the USA), there's really not much you can presuppose students know as they come in. I'm aware of this mainly in connection with religion, of course, but today I discovered another and, in its way, more serious lacuna: basic economics.
In class we spent last week reading Max Weber's Protestant Ethic and the Spirit of Capitalism, and today we were talking about the continuing legacy of the vocation idea (I had students read the first few chapters of The Purpose-Driven Life), and I was feeling my way toward the suggestion that people have a quasi religious (or secularized) faith in the market - or did until recently! After a while it became clear that only 2 of the 13 students had any idea what the market is, or how it is thought to function. To them, capitalism is simply the rule of the rich. (While McCain-haters all, few could do better than his idea that "greed" is the cause of the present calamity.)
So I found myself at the blackboard trying to remember the rudimentary supply/demand curves crossing at an equilibrium point; with a little help from the two students who had learned about economics in high school, I got it right - even as I recalled that I didn't learn this in high school either (well, not in my American public high school). But just think... my students aren't more ignorant than most Americans. How many of my fellow citizens understand even this basic (however simplified) Econ 101 stuff?! How can they possibly make sense of the world?