The purpose of this study was to examine the influence of the social context, based within self-determination theory, on student's in-class physical activity. A total of 84 Year 11/12 physical education students were randomly assigned to one of three treatment groups; Autonomy-supportive, Controlling and Balanced. Data were collected using a pretest/posttest design measuring in-class physical activity. Analysis of data used Repeated Measures ANOVAs to examine group differences. Results indicated significant differences for students engaged in the autonomy-supportive context in terms of moderate-to-vigorous physical activity. These results indicate that instructional behaviors that align with an autonomy-supportive context can facilitate higher levels of in-class physical activity. (Contains 3 tables and 3 figures.)