Core school enrollment and staffing data from the historical file of the National Catholic Educational Association (NCEA) are presented for 1990-91 and for some previous years (typical comparisons are made with data for 1982-83 and 1989-90). The following demographic trends that influence both public and private education are summarized: (1) United States population trends; (2) school-age populations; (3) enrollment in public and private schools; (4) teachers and student-teacher ratios; (5) characteristics of private schools; (6) statistics on Catholic education; (7) Catholic school enrollment; and (8) staffing of Catholic schools. Data for 2,475,439 students in 8,587 Catholic schools in 1990-91 are presented. Comparisons are made with other private schools and the public sector. Data were submitted by 174 archdiocesan and diocesan offices of education and, in some cases, state Catholic conferences, representing 100% of Catholic schools. The data are presented in 21 exhibits, which include 18 graphs, 18 tables, and 1 figure. Appendix A lists Catholic school statistics by state and diocese or archdiocese. Appendix B lists enrollment increases by state. (SLD)