This paper traces the development of cooperative learning strategies in the practices of two middle school mathematics teachers who implemented an innovative mathematics curriculum with their 7th and 8th grade students. The evidence suggests that these teachers increased their use of cooperative learning strategies, and this increase was related to the nature of the curriculum materials, as well as to their views of the nature of mathematics and its teaching and learning. Moreover, both teachers appeared to share a similar view of the social context of the classroom. Contains 18 references. (Author)