Purpose: To examine the influence of negotiations between students and graduate teaching assistants (GTAs) on GTAs' instruction within university physical activity classes. Method: Participants were 10 GTAs working in one university. Data collection and analysis were guided by constructs from the classroom ecology paradigm. Data collection techniques employed were non-participant observation, informal and formal interviews, and document analysis. Data were analyzed using analytic induction and constant comparison. Results: The type, focus, and extent of negotiations in GTAs' activity classes varied considerably depending on whether or not they had received prior pedagogical training, gained experience of teaching physical education in schools, and were familiar with the content. Conclusion: Our findings suggest two courses of action be taken if quality activity courses are to be delivered. First, such classes should be taught by GTAs with pedagogical training and teaching experience. Alternatively, previously untrained and inexperienced GTAs should be given extensive preparation.