The purpose of this study was to better understand the nature and extent of students' understanding of Newtonian physics. This study investigated differential effects of three different instructional treatments (computer text instruction [CTI], computer text-graphic instruction [CTGI], and computer-based instruction [CBI]). These treatments exposed areas of the subjects' lack of understanding of physics concepts that were measured by the Force Concept Inventory (FCI) to determine students' misunderstandings of Newtonian physics concepts. The sample consisted of 90 undergraduate students with non-physics majors enrolled in the physics for life science course at a comprehensive university in the Southwest. The results indicate that students who used the CBI lesson did significantly better than students using the CTGI or CTI lessons with respect to understanding Newton's laws. In addition, students who used a more meaningful learning approach did not necessarily have higher reasoning abilities.