We’ve looked at contemporary grades from over 160 colleges and universities in the United States with a combined enrollment of over 2,000,000 students and historical grades from over 80 schools... The rise in grades in the 1960s correlates with the social upheavals of the Vietnam War. It was followed by a decade period of static to falling grades. The cause of the renewal of grade inflation, which began in the 1980s and has yet to end, is subject to debate, but it is difficult to ascribe this rise in grades to increases in student achievement.
In a companion piece, the authors discuss these trends in detail, compare the sciences to the humanities, and note that the same trend is not evident in community colleges. Of particular interest are links to the data from over 200 colleges and universities. At my college the GPA was 2.7 in the mid-1960s, and is now nearly 3.5.