This study examined the effects of differential grading in science, technology, engineering, and mathematics (STEM) and non-STEM fields over eight consecutive semesters. Using data from 62,122 students at 26 four-year postsecondary institutions, students were subdivided by institutional admission selectivity levels, gender, and student major categories (SMC): STEM-Quantitative, STEM-Biological, and non-STEM. Estimated mean differences (d) in semester grade point averages (GPAs) between groups were calculated over eight semesters using meta-analytic techniques. Within the same gender and institutional admission selectivity level, the average GPA of STEM majors was higher than that of their non-STEM counterparts in the first semester, but average GPA gaps generally decreased over the following semesters. Practically significant differences extended beyond the first year for most of the STEM-Biological versus non-STEM comparisons, however. Institutional admission selectivity and gender moderated the results for the STEM-Quantitative versus non-STEM comparisons and the STEM-Biological versus non-STEM comparisons. Given the differences in male and female participation rates within the STEM fields, gender comparisons were also conducted. The average GPA of female students was higher than the average GPA of male students, but SMC and admission selectivity moderated the results. The STEM-Biological semester GPA comparisons generally indicated no practically significant differences between male and female students' average GPAs. Supplemental tables are appended.