Effects of ethnic/racial diversity among students and faculty on cognitive growth of undergraduate students are estimated via a series of hierarchical linear and multinomial logistic regression models. Using objective measures of compositional, curricular, and interactional diversity based on actuarial course enrollment records of over 6,000 students at a public research university, the study finds no patterns of positive correlation with objective measures of cumulative academic achievement (i.e., final graduating GPA, GRE/GMAT test scores, graduate school enrollment) net of academic preparation at college entry and socio-demographic background, and with or without accounting for academic major, college curricular experience, and financial aid. Results are consistent with student self-assessed level of critical thinking skills after graduation, but not with self-assessed level of understanding of racial and cultural issues, both affective outcomes showing a positive correlation with curricular diversity. As the findings contradict most of the higher education literature on survey-based cognitive benefits of ethnic/racial diversity, the study calls for use of objective measures to advance the research in this area. (Contains 19 tables, 4 graphs and 10 footnotes.)