A study sought to determine the stability of student/teacher interactional gymnasium behavior over one academic year. The design of the study was a single-subject, time-series analysis. The subject was a male elementary school physical education teacher with 14 years of experience. Data were collected using the Cheffers Adaptation of Flanders Interaction Analysis System (CAFIAS) with observations made at equally spaced intervals throughout one school year. A total of 52 useable observations were obtained and analyzed to determine behavioral stability. Only one-quarter of the CAFIAS behavior categories were found stable and these behaviors accounted for less than 30 percent of all behavior. This led to the conclusion that teaching behavior in this physical education setting may lack the stability necessary for making inferential generalizations common to the natural science paradigm used in research into teacher behavior. It is concluded that teaching may be a social rather than a natural phenomenon. The results of both this study and previous research found that teaching behavior fluctuates in unpredictable patterns, and additional research paradigms, along with natural science methodologies, may depict a more accurate and complete picture of teaching in the gym. The study suggested a need for more long-term investigations of teaching. (JD)