The New York Times' Economix blog featured a study out of Furman University, which shows that beginning in the 1960s, GPAs at national colleges and universities rose at a pace of one-tenth of a point per year, from an average of 2.52 in the mid-'50s to 3.11 in the mid-'00s. Interestingly, during the past 50 years, GPAs at private schools have wandered upwards at a faster rate than at public schools.
Today, the average public college student sports a 3.0 GPA; whereas the average private school student tallies a 3.3. The authors say that the grade inflation discrepancy is likely responsible for the overrepresentation of private college graduates at top pre-professional graduate programs.
There are, of course, some exceptions to the trends, the author's note (PDF):
Not all schools follow the patterns above. There are many that grade significantly higher and lower than their peer schools. Applying the formulae above to observed grades, we can look at how well schools deviate from predicted grading. Private liberal arts colleges have considerable variability from that predicted by the two equations above, particularly on the low end. Public flagship schools are significantly positively skewed in their grading relative to other public schools. What is perhaps most striking is that science and engineering schools – the MITs and Georgia Techs of academe – grade on average about 0.15 lower than their non-science and engineering peers. This may be why these schools tend to have lower retention levels; it also means that their graduates are disadvantaged in terms of their post-graduate prospects.