Growth during the last 2 years of high school was examined in public and Catholic high schools using data from the High School and Beyond database--a large, nationally representative study. Earlier research was extended by considering: (1) affective variables (e.g., self-concept, locus of control), academic choices (e.g., course selection), and postsecondary activities as well as academic achievement outcomes; (2) Catholic single-sex and Catholic coeducational schools separately; and (3) academic self-concept, school policies related to discipline, and academic orientation as mediating variables. Data for 4,378 students from public schools, Catholic coeducational schools, Catholic boys schools, and Catholic girls schools were analyzed. A sample size of 4,000 was used to test statistical significance in all analyses. Results indicate that growth in the last 2 years of high school on a variety of outcomes was modestly larger for Catholic school students than for public school students. Effects favoring Catholic schools were relatively larger for the selection of academic courses, relatively smaller for achievement and university attendance, and almost zero for affective variables. Subsequent analyses suggest that Catholic schools encourage students to take more academically challenging coursework and that this difference explained other public/Catholic differences. Three tables contain study data. A 49-item list of references is included, and an appendix defines the variables considered. (Author/SLD)