Harvard University has this year awarded far fewer top grades after it was embarrassed last year by the disclosure that almost all its students received them.
But more than half of all Harvard students still receive the very highest or second-highest possible grades.
The revelation last year that the distinction of "honours" was being handed out to almost every Harvard graduate brought about a national debate about grade inflation and forced faculties at Harvard and elsewhere to change their grading scales.
The decline in the number of top grades awarded at Harvard, however, began before that time, indicating that professors were already conscious of the trend and were trying to do something about it.
"I am pleased to see that last year was a year of grade deflation, and look forward to increased attention to grading practices," said Harvard president Lawrence Summers, who called grade inflation "a matter of great concern".
At Harvard, students are graded on a scale of A to D. Grade F indicates a fail. The number of As fell last year from 48.4 per cent to 46.4 per cent; the number of Bs rose from 40 per cent to 42.1 per cent.
Some critics argued that the change was barely statistically significant.
And in a separate development, a Duke University researcher released a study of grades at 34 universities and colleges showing that grade inflation has persisted at all types of institutions.
Researcher Stuart Rojstaczer said: "The resurgence of grade inflation in the 1980s principally was caused by the emergence of a consumer-based culture in higher education.
"Students are paying more for a product every year, and increasingly they want and get the reward of a good grade for their purchase. In this culture, professors are not only compelled to grade easier, but also to water down course content. Both intellectual rigour and grading standards have weakened."