For open-mindedness to be an Aristotelian personal virtue, its possession must make agents better off. Unfortunately, open-mindedness does not currently pay. The reasons include (1) "novelty glut" -- taking seriously even a tiny percentage of the worthwhile, available ideas would be overwhelming; and (2) "deception campaigns" -- we lack the time, sophistication, and knowledge to uncover the truth ourselves. Our best coping strategy is closed-mindedness, that is, to ignore whatever we encounter unless vouched for by trusted experts. However, as Jessica Gottlieb and Howard Curzer argue in this article, student learning demands open-mindedness. Although open-mindedness is a personal vice, it is a student-role virtue. Thus, teachers must buffer their classrooms against those features of the contemporary world that make open-mindedness counterproductive. Teachers can counter these threats by using "core practices" that are general (such as facilitating classroom discussions) and content-specific (for example, engaging students in scientific investigations). Core practices enable teachers to craft environments and experiences that make open-mindedness great again.