This study analyzed data from the Wabash National Study of Liberal Arts Education to estimate the unique effects of exposure to classroom diversity and involvement in interactional diversity on growth in critical thinking skills during the first year of college. Net of important confounding influences, neither classroom nor interactional diversity had significant general effects on critical thinking. However, interactional diversity did positively influence critical thinking skills for White students and for students who were the least well prepared academically for college. (Contains 3 tables.)