It is known that introductory physics students rarely, if ever, read the textbook prior to coming to lecture. In this study, we report results from a curriculum intervention in a large enrollment introductory physics class that addresses this problem. In particular, we introduced web-based multimedia learning modules (MLMs) as a "prelecture assignment" designed to better prepare students before coming to lecture. We used student performance on "preflight questions" that they answer prior to lecture as a measure of their before-lecture understanding of the physics concepts. We found significant improvement in student performance and on the vast majority of these preflight questions as compared to that from previous semesters in which MLMs were not available. We found significant improvement for all students, independent of their background or ability level. (Contains 5 figures and 1 table.) [A 14-item list of references and notes is provided.]