Some issues in defining dropouts and reporting information about them are explored, with reference to the Common Core of Data (CCD) survey of the National Center for Education Statistics. There has not been any uniform national count of how many students leave school, and no commonly accepted definition has been developed that allows a number to be ascertained. The definition used in the 1989-90 field tests of dropout statistics collected for the CCD provides operational criteria for identifying dropouts. For example, deceased, incapacitated, or currently suspended students are specifically removed from consideration. Factors to consider include whether a student is engaged in an elementary/secondary program, as opposed to adult education, and whether a completed credential will be recognized by state or district officials. Those who conduct research or provide dropout statistics need to make their definitions explicit. One figure shows the CCD "decision tree" for classifying dropouts, and one table illustrates a classification worksheet. (SLD)