Research

http://web.ebscohost.com/ehost/detail?vid=6&hid=122&sid=3509a59f-4f98-4c57-851e-b66e11ed466a%40sessionmgr11&bdata=JnNpdGU9ZWhvc3QtbGl2ZQ%3d%3d#db=eric&AN=EJ780518
This document covers the system in which high schools rank students. Test scores, difficulty of courses, class rank, and grade point average are the top four indicators of student success when applying to universities. In the study, 80% of high schools use a weighted GPA to determine rank, 12.6% determine rank with an unweighted GPA, 5% use both, and 2.4% use no class rank. Some school districts implement a bonus unweighted where AP/ honors classes have an additional "weight" to the unweighted GPA. In addition, many large schools are faced with numerous Valedictorians due to ties in GPA for number one in class rank.
Class rank is seen to "provide colleges with a measure of relative class standing [and] to provide the student with extrinsic incentives to take appropriately challenging courses while in high school to adequately prepare the student for a college curriculum". Both are means to increase course difficulty for students in order to challenge themselves and force them to grow.