ABSTRACTIn this study I explored how elementary school students are initially assigned to homeroom classrooms (criteria used and heterogeneous vs. homogeneous grouping), subsequently assigned to mathematics classes (e.g., self‐contained, regrouped, departmentalized), and grouped for mathematics instruction within classes (e.g., whole‐class, two groups, individualized). This three‐dimensional typology of school and classroom organization was used to survey 571 elementary school principals from 12 states. Results showed that students were generally assigned to heterogeneous self‐contained homeroom classes, that they remained in these same classes for mathematics, and that mathematics was usually taught to entire classes (whole class). Within‐class ability grouping, within‐grade regrouping, and departmentalized plans were used increasingly for mathematics at the intermediate grades, but across‐grade or Joplin Plan programs were infrequent.