To determine the factors contributing to the widely reported increase in average undergraduate grades, data were analyzed from students from two different time periods: 22, 792 students in the mid-1980s and 29,464 in the mid-1990s. After controlling for student background characteristics and institutional characteristics, it appears that undergraduate grades increased across different types of institutions and major fields, but the increases were not of the same magnitude or due to the same factors. Evidence of grade inflation was found only at research universities and selective liberal arts colleges, while grade deflation occurred at general liberal arts colleges and comprehensive colleges and universities and in the humanities and social sciences. Also contributing to the increase in grades were changes in student characteristics and subtle adjustments in grading reward structures at all institutional types and for all major field clusters. In general, grading reward structures favored White students, female students, and upper-division students. Equally important, students 'academic effort was rewarded consistently across time at all institutions and major fields, with students who invested more time and effort in their studies reporting higher grades.
