We consider the response to incentives as an explanation for productivity differences within a firm that paid its workers piece rates. We provide a framework within which observed productivity differences can be decomposed into two parts: one due to differences in ability and the other due to differences in the response to incentives. We apply this decomposition to male and female workers from a tree-planting firm in the province of British Columbia, Canada. We provide evidence that individuals do react differently to incentives. However, while the women in our sample reacted slightly more to incentives than did the men, the average difference is not statistically significant. The productivity differential that men enjoyed arose because of differences in ability, strength in our application.