Meta-analytic techniques were used to examine the effectiveness of Web-based instruction (WBI) relative to classroom instruction (CI) and to examine moderators of the comparative effectiveness of the 2 delivery media. The overall results indicated WBI was 6% more effective than CI for teaching declarative knowledge, the 2 delivery media were equally effective for teaching procedural knowledge, and trainees were equally satisfied with WBI and CI. However, WBI and CI were equally effective for teaching declarative knowledge when the same instructional methods were used to deliver both WBI and CI, suggesting media effects are spurious and supporting Clark's (1983, 1994) theory. Finally, WBI was 19% more effective than CI for teaching declarative knowledge when Web-based trainees were provided with control, in long courses, and when trainees practiced the training material and received feedback during training. Study limitations and directions for future research are discussed.