Every teacher has a few favorite assignments. Here's one of mine, which I gave to two undergraduate software engineering classes that I taught at the University of Toronto:
According to Statistics Canada, about 6% of Canadians are from East Asian or South Asian backgrounds. However, roughly 75% of students in Computer Science are ethnically Asian. Your task is to write two short essays, each roughly 1000 words long. In the first, you are to argue that this proves Caucasians and members of other ethnic groups are intrinsically less interested in or capable of programming than Asians. In the second, you are to argue that it doesn't prove this.
Some students said the exercise made them feel uncomfortable, and no one ever seriously claimed to believe the "more capable" position. This led to some heated discussions after essays were graded and handed back when I asked them why they believed this imbalance didn't mean Asians were naturally better at programming than Caucasians, but so many of them did believe a (lesser) imbalance between men and women implied that. I'd be interested to hear from anyone else who's tried something like this in a class.