Concern about the thoroughness of surveys conducted by the National Center for Education Statistics (NCES) to collect descriptive data on the nation's nonpublic elementary and secondary schools prompted the NCES to conduct a validation study. A stratified random sample of 21 geographic areas was selected. Site visits were made to six of these areas and long-distance methods were used to search the rest. The study focused on the non-Catholic sector of private education because the list of Catholic schools was believed to be reasonably complete. Of almost 20,000 schools included in the NCES survey lists, 277 were located in these sampling areas. Several methods were employed and compared for seeking previously unlisted schools. These methods were based on governmental requirements for registering schools, the use by schools of advertising, linking relationships with other religious and educational organizations, and public school records of student transfers to nonpublic schools. This report discusses the study's findings related to the reliability of NCES private school lists, the growth of private schools, the reliability of data from the original and more recent surveys, and effective methods for identifying schools. Appendixes--half of the report--provide supplementary tables and individual site reports for the six sites visited. (PGD)