To implement cooperative learning successfully in practice, teachers require knowledge of cooperative learning, its features and terms, and how it functions in classrooms. This qualitative study examined 12 Australian generalist primary teachers', understandings of cooperative learning and perceived factors affecting its implementation. Using Johnson and Johnson's (1994) features of cooperative learning and Bain, Lancaster and Zundans' (2009) list of cooperative learning terms as a framework for analysis, we found that teachers' level of cooperative learning knowledge shaped their perceptions of the factors affecting its implementation in the classroom. The study supports the need for a deep embedding of cooperative learning pattern language in teacher training and professional development courses, and highlights the ongoing challenge of translating educational theory into effective practice on a larger scale in schools.