College graduates do not always pursue careers related to their major. Science majors working in jobs unrelated to their field of study earn approximately 30% lower wages than those working in related jobs. We develop a structural model of major choice and labor market outcomes that allows for skill uncertainty and differential accumulation of human capital across major. Our findings confirm that the average return to obtaining a science degree and working in a related job remains close to 30%. We also find that individuals are uncertain about their future productivity at the time of the college major decision.