Motivating students to come prepared to class is often a futile exercise. The consequences are magnified as more instructors adopt the flipped classroom teaching model, in which students are expected to come to class with some knowledge of the material. This paper analyzed the implementation of a pedagogical tool that addresses this problem: multimedia pre-lectures. We tested the efficacy of pre-lectures on students with no prior exposure to college or AP-level economics using a controlled clinical experiment, focusing on introductory economics concepts. Students who had access to pre-lecture materials scored significantly higher on comprehension and retention than those with access only to textbooks.