Associate Professor of Economics Ann Owen presented "Grades, gender, and encouragement: A regression discontinuity analysis" at the American Economic Association meetings in San Francisco on January 4. In this paper, Owen found evidence that female students who receive an "A" for a final grade in an introductory economics class have a meaningfully higher probability of majoring in economics. 

Because the technique used in the paper, regression discontinuity analysis, looks for differences in outcomes for students who in other ways should be very similar, this finding is fairly strong evidence that grades have an encouragement effect for female students. Owen found no evidence of a similar effect for male students.