A constant theme of reports about math and science is that the United States will have a large enough supply of scientists only if it does a better job of attracting black and Latino scientists -- and not just relying on Asian American, white and foreign talent. Many of these reports note that large shares of black and Latino high school students don't receive the kind of preparation they should in math and science.

A new study points to another factor: the role of black college instructors in encouraging black science students to persist as science majors. The study finds a statistically significant relationship between black students who plan to be a science major having at least one black science instructor as freshmen and then sticking to their plans. The finding could be significant because many students (in particular members of under-represented minority groups) who start off as science majors fail to continue on that path -- so a change in retention of science majors could have a major impact.

At the same time, the study did not find a similar impact based on gender.

The study was released by Cornell University's Higher Education Research Institute, which is sponsoring a conference this month on this research and other studies focused on why some students are more likely than others to persist as science and mathematics majors. The research on the impact of race and gender was conducted by Joshua A. Price, a doctoral student at Cornell who in the fall will join the economics faculty at the University of Texas at Arlington.

Price analyzed data on more than 157,000 students who enrolled as first-time freshmen in one of the 13 four-year universities in Ohio between 1998 and 2002 and who said that they intended to major in science, technology or mathematics. He then examined whether those black students who had a black instructor and female students who had a female instructor were more likely to stick with their planned STEM major than those who did not. For purposes of the study, "instructor" had to be the person -- typically but not always a professor -- who was responsible for a course. A black teaching assistant working for a white professor who ran a course would not count.

In doing his analysis, Price controlled for academic preparation using ACT scores so that the students of various races and genders were compared to those who shared their race and gender characteristics as well as their level of academic preparation.

And here he found that black students who had at least one black science instructor as freshmen were statistically more likely to continue on as STEM majors than those who did not. (He tried to see if there was an additional gain by having two math or science instructors taught by black instructors, but there were too few black science instructors to allow a large enough pool of students to have taken courses from two of them.)

On the issue of female students taking STEM courses from female instructors, Price found that these students were slightly less likely than others to continue as STEM majors, but the decline was so small that it was not statistically significant. He found no impact on the persistence rates of white students who took a course with a black instructor or male students who took a course with a female instructor.

One other finding was that black STEM students were more likely than white students to end up in STEM courses or sections led by black instructors, again suggesting a key role for these black science professors. Price writes in his study that he tried to control for this by factoring in the overall odds of students ending up with black and white instructors.

In the paper, Price writes that while previous studies have found positive educational benefits for minority students having same-race teachers in elementary and secondary schools, this paper goes further than other previous research in higher education. "These results suggest that policies to increase the minority representation among faculty members might be an effective means of increasing the representation of minorities who persist and ultimately graduate within STEM fields," he writes.

In an interview, Price said that much more research was needed before trying to base public policy on these or similar findings. He said that there are some key questions that still need to be explored that could have an impact on any policies. He said, for example, that the impact of having a black instructor could come from a "role model effect" or from a mentoring effect.

If the impact is from role models, it would be essential to have more black scientists around -- even if students aren't enrolled in their courses, they might benefit from seeing black professors, he said. If, however, the impact is from black instructors being better mentors of black students, that would raise questions of whether all professors could be taught to be better mentors to black students.

He also said that he was not sure his findings on women should be seen as questioning the need to hire more female scientists. He said that some recent research about the impact of instructor gender on students suggests that the greatest impact of same-gender instructors is on high-achieving female students, and he said his pool did not have enough differentiation to see if there was more of an impact on this group of students.