The purpose of this study was to examine how learners with different levels of prior understanding of a topic interact and learn from computer-assisted video instruction systems when they have control of content, sequence, pace, and mode of instruction. Based on pretest scores, 80 subjects were randomly selected, half with low prior conceptual understanding, and half with high prior conceptual understanding. Half of the subjects from each group were randomly assigned to a program vs. learner control treatment which consisted of computer-assisted video instruction modules on protein synthesis. A 2X2 analysis of variance was conducted on posttest scores and time on task, followed by a regression analysis to assess the relationship of other independent variables with posttest scores and time on task. In the learner control condition, subjects with high prior conceptual understanding in the subject area made significantly better use of control options and their time than did subjects with low prior conceptual understanding. In the program control condition, there were no significant posttest score differences, but there were significant time on task differences between subjects with low prior conceptual understanding and high prior conceptual understanding. Low prior conceptual understanding subjects had significantly higher posttest scores in the program control condition than in the learner control condition; however, there were no significant differences in time on tasks between conditions. Finally, high prior conceptual understanding subjects performed equally well in both program control and learner control conditions. A three-page list of references and several tables/figures complete the document. (Author/JB)