Despite expectancy theory’s widespread appeal and influence as a framework for motivation in organizational and educational settings, studies that have examined the theory’s validity for performance-based outcomes, particularly with academic performance as the criterion, have been characterized by inconsistent results. Given numerous methodological concerns associated with past studies (e.g., prevalence of between-person rather than within-person design), we examined the predictive validity of expectancy theory for academic performance using methods that were consistent with the theory’s original conceptualization. Additionally, we assessed the validity of the theory for students’ study effort. The final sample included 123 undergraduate students who reported their final grades in four courses. Study effort and other variables were measured with self-report surveys. Because course grades were nested within each person, multilevel modeling was used to test study hypotheses. Both the valence model and the force model predicted a student’s current study effort, but contrary to expectations, neither model predicted a student’s final course grades. In contrast, both valence for academic success and the simplified force model (based only on valence and expectancy) predicted current study effort, final course grades, and explained incremental variance beyond cognitive ability. Furthermore, the predictive validity of this force model was relatively stable across the 11 weeks of the study. Based on methods congruent with expectancy theory’s original framework, we find that the force model does not predict academic performance. An alternative version of the model, however, predicts course grades and has incremental validity over cognitive ability. Our results have several significant theoretical and practical implications.