Collaborative teaching and learning is advocated by many reformers of mathematics education (Schwan Smith, 2001). However, in most schools and classrooms teachers work and students learn solo. In this study Dr. Berry investigates the work done by two teams of elementary teachers as they designed classroom tools to help them support and enhance their students working in groups solving open-ended thought revealing activities (Lesh, Hoover, Hole, Kelly & Post, 2000). This research reveals the teachers'' interpretations of their role in supporting and enhancing students'' functioning well in groups. These interpretations are described as they are expressed in the form of two instruments designed for optimizing those roles, a group observation tool, and a teacher self-coaching tool. The teachers participated in a design research study (Collins, 1992) that included an iterative series of three situations where they expressed, tested, and revised those interpretations. This book reveals the tested and refined tools that the teams produced which expressed their ways of thinking, and the themes and trends of thinking across the development of those tools.