The Class Rank Update processes only those students who have a Class Code. Thus, for accurate rankings, you need all students to have a Class Code. The Class Code is updated by the Classification Update process and stored on the Student Term Summary by Division table (stud_term_sum_div.class_cde). The Class Code is visible on the Student Inquiry window, Summaries tab, Division subtab, Classification column.

(The Class Rank Update also requires a Division Code, but that's almost never empty.)

See the Class Rank Update Process topic for important details on how to run the process.