How can we improve the instructional effectiveness of an online slideshow lesson? In the present study, college students received a 12-slide multimedia slideshow lesson on how a geographic information system works. In a 2 × 2 design, the lesson was presented one complete slide at a time (large segment) or added one section of the slide at a time (small segment) when the student pressed the CONTINUE key, and the words were presented in printed form (text) or spoken form (voice). Students performed significantly better on a transfer posttest when the lesson was paced in small segments rather than large segments (d = 0.34); there was no effect or interaction involving modality. The small-segment version was rated as less difficult than the large-segment version (d = 0.43). The segmenting principle was supported in the context of online slideshows.