Many scholars have argued that motivation is dynamic and malleable across time and contexts. In this article, we investigated changes in undergraduates' task value and self-efficacy across an academic semester. Sixty three undergraduate students completed the Motivated Strategies for Learning Questionnaire across five time points in their introductory educational psychology class. We predicted that, across the semester, students' expressiveness of these constructs would change. Using growth curve modeling, we found both constructs to fluctuate in a cubic fashion. The implications of these findings are discussed.