Excessive entitlement--an exaggerated or unrealistic belief about what one deserves--has been associated with a variety of maladaptive behaviors, including a decline in motivation and effort. In the context of tertiary education, we reasoned that if students expend less effort to obtain positive outcomes to which they feel entitled, this should have negative implications for academic performance. We tested this hypothesis in a naturalistic experiment in a large course, in which students' self-reported entitlement attitudes (measured at the beginning of the semester), the idiosyncratic difficulty of the class, and several other individual difference variables associated with academic achievement (personal responsibility, frustration intolerance, and locus of control) were used to predict final exam performance. As expected, greater entitlement was associated with poorer final exam marks, particularly among students for whom the class was objectively challenging. Although no other personality variable qualified the interaction, the extent to which students accepted responsibility for their performance mediated the main effect of entitlement, while external locus of control independently predicted poor exam performance.