The historical productivity data from the Hawthorne experiments permit the statistical evaluation of the hypotheses of the original experimenters and others by conducting appropriate time-series analyses. In this paper a recent hypothesis by H. M. Parsons that the output trends in the first relay assembly test room experiment were due primarily to increased skill and competence is evaluated empirically by fitting a standard learning equation to the data for each operator. The learning equation describes the overall data trends very well. Then, to assess the effects of the experimental manipulations and variables hypothesized by other investigators, the productivity data are detrended of the learning effect and the detrended data are analyzed. This analysis shows that the introduction of rest pauses in the test room led to the more productive use of work time. Overall, it appears that the conditions motivating increased learning—i.e., improved reinforcement conditions (increased status and new economic incentives) and regular performance feedback —were the primary causes of increased output.