In this study, 364 first-year physics students were randomly assigned to one of four online multimedia treatments on Newton's First and Second Laws of Motion: (1) the "Exposition", a concise lecture-style presentation; (2) the "Extended Exposition", the Exposition with additional interesting information; (3) the "Refutation", the Exposition with common misconceptions explicitly stated and refuted; or (4) the "Dialogue", a student-tutor discussion of the same material as in the Refutation. Students were tested using questions from mechanics conceptual inventories before and after watching the multimedia treatments. Results show the Refutation and Dialogue produced the greatest learning gains, with effect sizes of 0.79 and 0.83, respectively, compared with the Exposition. Students with low prior knowledge benefited most, however high prior knowledge learners were not disadvantaged by the misconception-based approach. The findings suggest that online multimedia can be greatly improved, promoting conceptual change in students with all levels of experience, by including a discussion of misconceptions.