Student evaluation of teaching (SET) is important to faculty because SET ratings help faculty improve performance and are often used as the basis for evaluations of teaching effectiveness in administrative decisions (e.g., tenure). Researchers have conducted over 2,000 studies on SET during the past 70 years. However, despite the explosive growth in online education during the past decade, researchers have largely neglected the use of SET to evaluate teaching effectiveness in online courses. This exploratory study analyzed the actual SET data collected during a single semester at a large mid-western college that offers over 250 online/Web-based classes. The data included five dependent and eighteen independent measures of teaching effectiveness. The results indicate that average SET ratings in online classes are significantly lower than the average ratings in on-campus classes across all five dependent measures. This finding offers preliminary empirical support for anecdotal evidence cited by earlier authors in this field. Furthermore, regression analysis of the full model for each dependent variable indicated that the independent variables explained a significant portion of the variance in SET ratings. Examination of the standardized beta coefficients revealed that the strength and significance of the independent variables varied across the five dependent measures. Findings also indicate that organization of the course materials had a strong impact on all five measures of overall teaching effectiveness. Other variables including clarity of the instructor’s writing, timeliness in providing feedback, and interest in whether students learned were also significant factors in models that measured instructor effectiveness (as opposed to models that measured quality of course content). The paper concludes with a discussion of the implications of this study for administrators, faculty, and researchers.