It’s easy to get focused on how much students don’t know. We all have stories—such as my student who, when I said “paradigms,” heard “pair of dimes”—that we laughingly share with colleagues. Much more serious is the absence of all sorts of essential information and basic skills, and how not having them threatens academic survival. Knowing what students don’t know and can’t do saves us from making erroneous assumptions. We can move directly to teaching that helps students fill in those gaps.