In 2 experiments, mechanically naive college students viewed an animation depicting the operation of a bicycle tire pump that included a verbal description given before (words-beforepictures) or during (words-with-pictures) the animation. The words-with-pictures group outperformed the words-before-pictures group on tests of creative problem solving that involved reasoning about how the pump works. In a follow-up experiment, students in the words-withpictures group performed better on the problem-solving test than students who saw the animation without words (pictures only), heard the words without the animation (words only), or received no training (control). Results support a dual-coding hypothesis (Paivio, 1990) that posits two kinds of connections: representational connections between verbal stimuli and verbal representations and between visual stimuli and visual representations and referential connections between visual and verbal representations.A major goal of science is to provide explanations for how various physical, biological, and social systems work. It follows that a major goal of science education is to help students understand scientific explanations. What constitutes an understandable explanation? How can educators help sciencenaive students to understand scientific explanations? In particular, how can computer-based animations be used to promote scientific understanding? These are the issues addressed in this article.Preliminary information regarding these questions is provided by previous studies on the relation between explanative text, that is, step-by-step descriptions of cause-and-effect actions occurring within a system, and explanative illustrations, that is, frame-by-frame pictures of the cause-and-effect changes occurring within the system, in helping students to understand scientific explanations (Mayer, 1989a(Mayer, , 1989bMayer & Gallini, 1990). Students read passages on topics such as how pumping systems work, how braking systems work, or how electrical generation systems work and then answered creative problem-solving questions such as how to improve or troubleshoot the system. Some students read passages that contained explanative text followed by explanative illustrations (i.e., words before pictures); others read passages that included explanative illustrations with verbal labels corresponding to each step in the explanative text (i.e.,