The New York City Public School System has mandated an Integrated Student Data System (ISDS). This integrated system will include data already maintained in independent computerized files, as well as data that have not been computerized in any systematic way. This paper explores general issues about data accuracy for a system that covers all the students in the school system and that will include information required for a very wide range of functions. The paper develops three major themes. The first is that the need for data accuracy depends upon the use for which the data are intended. A second theme is that data system participation must be encouraged, for instance by maximizing the "fit" between the data system and the day-to-day operation of the school. The final theme is that the ISDS must ensure timely submission by schools of accurate data, that performance must be monitored, and that it must be possible to provide feedback. For each subject, discussion of issues and complications yield operating principles and guides for action. (Author/MLF)