In the present study, we explored why interspersing quantitative details through a multimedia lesson detracts from learners' qualitative understanding. Three experimental conditions were created. In each, participants had to study a qualitative text on the formation, propagation, and dispersion of ocean waves. In the concise condition no quantitative details were added to the text; in the expanded-interspersed condition, quantitative details were interspersed throughout the text; and in the expanded-after condition, quantitative details were provided after the text. The results showed that qualitative understanding was poorer in the expanded-interspersed condition than in the concise and the expanded-after conditions, with no difference between the latter two conditions. Furthermore, reading time of the qualitative text was comparable across the three conditions. By contrast, reading time of the quantitative information was lower in the expanded-interspersed condition than in the expanded-after condition. These findings are interpreted in terms of a disruption hypothesis. (Contains 1 table.)