In this study, the authors investigated co-learning between cooperating teachers (CTs) and their preservice teachers (PSTs). Using frame analysis, the authors contrast three problems-of-practice addressed by 23 dyads: problems of developing novice teachers, problems of improving teaching, and problems of improving student learning. The authors describe ways in which knowledge became shared, actors assumed new roles, and new types of tools, activities, and forms of discourse emerged for contextualizing collective work. Based on this study, the authors propose three process measures: the quality of student discourse CTs and PSTs support, the quality of discussion among dyads about students’ ideas, as well as the quality of newly created or evolving social routines and tools.