As we have written before, private colleges and universities are by far the biggest offenders on grade inflation, even when you compare private schools to equally selective public schools.
There are charts and further information at the link. By the way:
…about 43 percent of all letter grades given were A’s, an increase of 28 percentage points since 1960 and 12 percentage points since 1988. The distribution of B’s has stayed relatively constant; the growing share of A’s instead comes at the expense of a shrinking share of C’s, D’s and F’s. In fact, only about 10 percent of grades awarded are D’s and F’s.
It’s worth trying to model that too.