We implement a field experiment to examine how part-time work attracts applicants with different quality and productivity levels than full-time work. In a large-scale recruitment drive for a data-entry position in Ethiopia, either a part-time or full-time job opportunity was randomly offered across villages. We find that the part-time work attracts a less qualified pool of applicants with a stronger preference for short work hours, who in turn exhibit lower productivity, all relative to the full-time work. Our preferred estimates show that this selection effect on productivity may explain up to half of the typical part-time wage penalty. A simple conceptual framework demonstrates that a lack of high quality potential applicants with a strong preference for short work hours could explain the experimental evidence. The results have implications for the selection effects of alternative work arrangements and for the gender pay gap.