This meta-analysis employs a theoretical framework in quantitatively synthesizing empirical studies that investigate the effects of distance education (DE) versus classroom instruction on undergraduate student achievement. Analyses of 218 findings from 103 studies were conducted according to how media were used to support DE pedagogy. The results indicate that the effect sizes for synchronous instructor-directed DE were consistent and not significantly different from zero; in asynchronous DE, media only supporting independent learning was generally less effective than media supporting collaborative discussion among students, although both subsets were significantly heterogeneous. Follow-up analysis of asynchronous DE findings was framed in terms of three patterns of interaction-student-content, student-instructor and student-student. (Contains 4 tables.)