This study examined to what extent teachers who choose to take a course about cooperative learning implement the innovation and which factors account for variation in use of cooperative learning in their classrooms. Nine female elementary teachers were observed and interviewed. Teachers were categorized as effective users, competent users, marginal users, and nonusers, based on frequency of use, degree and kind of adherence to characteristics of the cooperative learning model, types of activities used in cooperative learning lessons, and degree of incorporation of the language and ideas of cooperation into the classroom. Four categories of factors appeared to influence teacher implementation of cooperative learning: the principal, the teacher's approach to teaching, the teacher's perception of cooperative learning, and the amount and kind of continued involvement the teacher has with the innovation. Results of this study are felt to differ from previous research on change in three ways: the study provides a different point of view in terms of the kind of support from the principal that is important; some of the teacher characteristics that appear to be influential are not those identified in the literature; and collegial support does not seem to be necessary in the way indicated by previous studies. Recommendations for practice are outlined. (Contains 14 references.) (JDD)