This study investigated 4th grade students’ conceptions of principles of mechanics, specifically Newton’s laws, taught as an integral part of their physical education program. While integration of physical education and other subjects has been written about since the 1970s, almost no research has examined what students learn as a result of this integration. This research brings together integrated curriculum with research on student conceptions of subject matter. Information processing theory from cognitive psychology and literature on student conceptions provide the theoretical frameworks for this study by examining what children know and how they learn cognitive aspects of movement activities. Participants were 20 fourth-graders (12 girls, 8 boys) in a suburban elementary school in the northeastern U.S. in which the physical education teacher taught principles of mechanics, including Newton’s laws, as part of the regular physical education curriculum. Audiotaped, structured interviews were conducted at the end of the school year and were transcribed verbatim. Student answers for each law were summarized and compared to key points of Newton’s laws. Students’ conceptions of Newton’s Laws were, for the most part, incomplete. Students consistently identified and gave accurate examples of Newton’s third law (for every action, there is an equal and opposite reaction). Students accurately stated this law and applied it to their own movement,(e.g., “if you push down you jump more, [to] run faster you push back harder”). In contrast, students’ did not fully understand and could not apply Newton’s first (inertia) and second (force=mass x acceleration) laws. Only three students named the law of inertia and only one student was able to provide the equation for Newton’s Second Law (Force=Mass x Acceleration). Students had the alternative conception that if equal force was applied to two objects, the heavier object would have greater acceleration. Mechanical principles are often suggested as appropriate topics to be integrated into K-12 physical education curricula. Results of this study indicate that these 4th graders conceptions’ of these difficult and abstract laws are incomplete and because students were unable to go beyond a basic recitation, their conceptions generally were not helpful for predicting and analyzing the actions of objects when a force has been applied. Understanding students’ concepts, as well as alternative conceptions students hold, can assist teachers in structuring learning experiences that help move students to higher levels of sophistication in their knowledge and understanding of science-related concepts.Keyword(s): elementary education, interdisciplinary, research