Jeffrey Selingo:

Over the course of the past three decades, the A has become the most common grade given out on American college campuses. In 2015, 42 percent of grades were top marks, compared to 31 percent in 1988.
This trend of grade inflation—the gradual increase in average GPAs over the past few decades—is often considered a product of a consumer era in higher education, in which students are treated like customers to be pleased. But another, related force—a policy often buried deep in course catalogs called “grade forgiveness”—is helping raise grade-point averages. Different schools’ policies can work in slightly different ways, but in general, grade forgiveness allows students to retake a course in which they received a low grade, and the most recent grade or the highest grade is the only one that counts in calculating a student’s overall GPA. (Both grades still appear on the student’s transcript.)
The use of this little-known practice has accelerated in recent years, as colleges continue to do their utmost to keep students in school (and paying tuition) and improve their graduation rates. According to a forthcoming survey by the American Association of Collegiate Registrars and Admissions Officers, a trade group, some 91 percent of undergraduate colleges and 80 percent of graduate and professional schools permit students to repeat courses to improve a grade. When this practice first started decades ago, it was usually limited to freshmen, to give them a second chance to take a class in their first year if they struggled in their transition to college-level courses. But now most colleges, save for many selective campuses, allow all undergraduates, and even graduate students, to get their low grades forgiven