Metamotivational knowledge is a burgeoning area of study. It refers to people's knowledge about motivation, and it has been shown to contribute to motivation and behavioral outcomes. The current study bridges metamotivational knowledge with self-determination theory (SDT), one of the most prominent theories of academic motivation. SDT proposes self-determination as a critical aspect of academic motivation. The current study thus answers two questions: What do students know about self-determination in academic motivation, and how does this knowledge predict outcomes? Two studies with college student samples from diverse cultures (American and Chinese) seek to answer these questions. The results show that students generally believe self-determined types of motivation to be more normative, more effective for performance and more beneficial for well-being than non-self-determined types. This is generally accurate, with some exceptions (e.g., the tendency to underestimate the relative normalcy of certain types of self-determined motivation). Path analyses support the hypothesized mediation model, such that believing self-determined academic motivation to be more normative and associated with better outcomes in performance and well-being, on average, predicts students' higher performance and well-being via the mediation of self-determined academic motivation. The effects of the metamotivational knowledge of self-determination hold after controlling for needs support and satisfaction processes, supporting metamotivational knowledge as an intraindividual resource for academic self-determination. In general, the mediation effects hold for both cultures, and similarities and dissimilarities from cross-cultural comparisons of metamotivational knowledge are also interpreted. The current research paves the way for metamotivational knowledge interventions aiming to improve student self-determination.