Using a natural experiment which randomized class times to students, this study reveals that enrolling in early morning classes lowers students' course grades and the likelihood of future STEM course enrollment. There is a 79% reduction in pursuing the corresponding major and a 26% rise in choosing a lower-earning major, predominantly influenced by early morning STEM classes. To understand the mechanism, I conducted a survey of undergraduate students enrolled in an introductory course, some of whom were assigned to a 7:30 AM section. I find evidence of a decrease in human capital accumulation and learning quality for early morning sections.