We use a randomized field experiment to estimate a causal effect of part-time recruitment on labor productivity by identifying worker selection as a mechanism and using worker-level productivity data. In recruiting for data entry work in Ethiopia, we identify 6,236 eligible women and randomly assign them to part-time or full-time job opportunities. We find that applicants with lower ability are more likely to select into part-time arrangements. Other observable characteristics capturing demographics, socioeconomic status, and attitudes toward work and family barely explain the selection. Those recruited through part-time job opportunities exhibit significantly lower productivity as measured by data entry speed.