Objectives: There is a common trend to train physical education teachers and coaches in need supportive teaching behaviors, however, little research has been done with graduate teaching assistants (GTAs) in college and university physical activity programs. The purpose of this study was to test the effects of a need supportive teaching training program on GTAs' ability to promote need support in college and university physical activity courses.

Design: Longitudinal and correlational.

Method: Participants were twelve GTAs from a midsized southeastern university in the United States, trained to deliver instruction in a positive motivational climate via in-person meetings, self-study materials, and tri-weekly meetings with researchers.

Results: Multi-level modeling revealed that the learning environment created by the GTAs improved across the duration of the study, with most of the growth between baseline and the first four intervention data points. Partial correlations seemed to indicate that these changes were influential among students, as evidenced through measurement of perceived autonomy support and motivational regulations.

Conclusions: Results revealed that the behavioral change process was carried out quickly (from the beginning of the training), suddenly (rather than gradually), and then leveled off until the end of the semester. These results provide some promise in being able to effectively train GTAs to be need supportive in a relatively short amount of time.