WASHINGTON--Just a year after former Harvard president Derek C. Bok co-wrote a book championing the use of race in the university admissions process, two Harvard professors have released a survey which they say shows students believe diversity has had a positive impact on their education.

Gary A. Orfield and Dean K. Whitla, both professors at Harvard's Graduate School of Education, announced Wednesday the results of what they say is one of the first studies to directly link diversity to educational outcomes.

Orfield and Whitla hired the Gallup Organization to survey 1,820 students from the Harvard and University of Michigan law schools. Of those surveyed, about 90 percent of the students felt that diversity had a positive impact on their education.

"It was an educational process that affected everyone pretty deeply," said Orfield, who is co-director of the Civil Rights Project, the Harvard institute that sponsored the survey.

Nearly two-thirds of the respondents said that diversity improved class discussions, and roughly 62 percent said diversity clearly or moderately enhanced their ability to work more effectively and get along better with others.

But critics of the survey say that the questions of the impact of diversity on the students are vague.

"To say that most law students have benefited from diversity begs the question 'What is diversity?'" said Edward Blum, executive director of the Houston-based Campaign for a Colorblind America (CCBA), a non-profit organization that lobbies against racial preferences. "How do we know when we have achieved it?"

For the survey's purposes, Orfield and Whitla focused on racial and ethnic diversity.

Orfield contends that affirmative action in admissions is necessary in order to make up for past discrimination and to ensure an educated population.