The purpose of this study was to describe and interpret the instructional ecology of Cooperative Learning in elementary physical education classes. Data collection included a modified version of the task structure system (Siedentop, 1994), interviews, field notes, and a teacher's journal. T-tests of the quantitative data revealed that instruction time, management time, transitions, and wait time decreased significantly during the units and refining, extending, and applying tasks increased significantly. Cognitive/social tasks were observed consistently in every lesson and contributed to student learning. Inductive analysis and constant comparison were used to analyze the qualitative data (Patton, 1990). The researchers identified four main categories from this data: organization and management of students, roles, skill development, and strategizing. To promote individual accountability the teacher used task sheets, assigned Cooperative Learning roles, kept group sizes small, randomly chose students to demonstrate their competence, and asked students to teach their teammates skills and tactics. (Contains 1 table and 1 figure.)