We examine graduate student teaching as an input to two production processes: the education of undergraduates and the development of graduate students themselves. Using fluctuations in full-time faculty availability as an instrument, we find undergraduates are more likely to major in a subject if their first course in the subject was taught by a graduate student, a result opposite of estimates that ignore selection. Additionally, graduate students who teach more frequently graduate earlier and are more likely to subsequently be employed by a college or university.