The purpose of this study was to examine the influence of an intervention grounded in Self-Determination Theory on preservice teachers' instructional behaviors and the motivational responses of their students. A total of 62 preservice physical education teachers enrolled in a secondary physical education content and methods course were randomly assigned to either a treatment (n = 31) or a control group (n = 31). The study employed a pretest/posttest design and data were collected through: (a) observation of preservice teachers' instruction, (b) a survey measuring preservice teachers' perceptions of their autonomy support, and (c) a survey measuring secondary students' motivation. Data analysis used repeated-measures ANOVAs to examine differences between the groups. Results indicated significant changes in autonomy-support for both teachers and students exposed to the intervention.