Data reexamination is a critical component for any study. The complexity of the study, the time available for data base development and analysis, and the relationship of the study to educational policy-making can all increase the criticality of such reexamination. Analysis of the error levels in the National Institute of Education's Instructional Dimensions Study (IDS) revealed inconsistencies between the data gathered in the field and the data finally analyzed in the study. Most of these problems were traced to processing errors that could have been corrected before the data were analyzed. The results of the IDS data base reexamination indicate that spending additional time and effort to assure accuracy of the data processing techniques could have saved time and effort by eliminating the need to search for problems. This document briefly describes the basic purposes and the technical design of the IDS to clarify the processes used in this instance of data reexamination. Three examples of error-finding and error-solving are included. (Author/PGD)