Background: A good deal of evidence indicates that students' motivational beliefs and attitudes play a critical role in their academic success. Research studies on how motivational factors may help determine whether students remain in high school or drop out, however, are relatively few. More specifically, there is a lack of research examining the dynamics of whether students' motivational beliefs from earlier in high school might be used to predict their status as a dropout in their final year. Aims: The aim of the present study was to examine the mediating role of students' educational expectations in linking students' school motivation to their dropout status by utilizing a nationally representative dataset. Sample: The present study used data from the Educational Longitudinal Study of 2002 (ELS: 2002). The final sample consisted of 16,194 students, with approximately 54% White, 13% Black, 16% Hispanic, and 10% Asian students, and the rest were Native American, Hawaiian, multiracial, or of other races. Method: Structural equation modelling was employed to conduct the mediational analysis. Results: The results of the present study demonstrated that the relationships between student ability beliefs in math and English and student behaviour of dropping out were fully mediated by students' educational expectations. The results also revealed that student intrinsic value in math and English had significant indirect relations with student behaviour of leaving school through students' educational expectations. Conclusions: The results of this study suggest that explanations for student dropout status that rely solely on students' social background and school behaviours without considering their motivation are incomplete. The study expands the extant research by showing possible pathways that motivate students to persist in high school. These pathways are specifically rooted in students' ability beliefs and intrinsic interest in learning through their relationships with students' expectations for their education.