Economics students are more likely than others to act self-interestedly and less likely to behave cooperatively, behaviour which is rational from the viewpoint of many economic theories. Students in other disciplines may have another conception of wha t is "rational." The latter may be more likely to behave cooperatively and less likely to behave self-interestedly. We have been comparing the behaviour of students from different disciplines in simple ultimatum bargaining and prisoner's dilemma games. Our paper discusses some of the ways (...) in which different academic disciplines both reinforce and elaborate upon student's conceptions of rationality. (shrink)