Hierarchical linear modeling allowed the indentification of specific school characteristics and policies which help explain the relationship between social class and minority status with mathematics achievement, the relationship between social class and minority status with mathematics course enrollment, and school means for achievement and for course enrollment. Major explanatory variables which emerged from the present analyses as predictors of all of the relationships of interest, fall into a small number of categories. Results indicated that there are considerable differences between Catholic and public schools on these outcomes, differences which favor Catholic schools. These analyses show that three sets of factors can effectively explain those cross-sector differences: (1) variation in the social content of schools; (2) variation in the academic and disciplinary climate among schools; and (3) variation in curricular offerings and requirements. Previous research results concluded that Catholic schools induce consistently higher mean achievement and that mean course enrollment in their students must be somewhat refined. The Catholic schools' advantage in mean school mathematics achievement and the more equitable distribution of that achievement appears to be explainable by the described school-related factors. It was concluded that Catholic sector advantages are explainable by a reasonably modest set of school characteristics and policies. References, tables and figures are provided. An appendix shows the computer output from the hierarchical linear modeling program. (PN)