This study tested two theoretical models of instructor credibility as a potential mediator between instructors' classroom communication behaviors (nonverbal immediacy, enthusiasm, and homophily) and students' intentions to persist in college. Participants included 570 undergraduate students from three institutions in the South-Central United States. Results of structural equation modeling provided greater support for the partial mediation model, in which nonverbal immediacy had both direct and indirect effects on students' intent to persist, though instructor enthusiasm and homophily were fully mediated by credibility. Overall, students' perceptions of these three instructor behaviors accounted for 56% of the variance in credibility and 43% of the variance in intent to persist. Furthermore, this model proved to be invariant across ethnic groups (Caucasian, African American, and Hispanic), suggesting that these instructor communication behaviors may contribute to positive outcomes for virtually all students, regardless of ethnicity. (Contains 3 tables and 6 figures.)