This study tested two models of instructor credibility as a potential mediator of instructors' prosocial communication behaviors (e.g., confirmation, clarity, and nonverbal immediacy) and students' learning outcomes. Participants included 1,416 undergraduate students from four different institutions across the United States. Results of structural equation modeling provided greater support for the partial mediation model, whereby credibility partially mediated the effects of teacher confirmation and clarity on learning outcomes, though it fully mediated the effects of nonverbal immediacy. When combined, students' perceptions of all three prosocial behaviors accounted for 66% and 57% of the variance in credibility and learning outcomes, respectively. Among the more important implications of this research is the finding that confirming behaviors and clarity have both direct and indirect effects on student learning. (Contains 6 figures and 1 table.)