This study was part of a larger project aimed at investigating the implementation of interdisciplinary teaching linking measurement in mathematics with locomotor movements in physical education. The purpose of this study was to examine the collaborative approach used by a physical education teacher and second grade teacher to develop and implement an interdisciplinary unit. The literature suggests that effective collaboration among teachers is critical to making interdisciplinary learning meaningful for students and teachers (Cone et al, 1998; Stevens, 1994). Collaborative strategies have been defined (Cone et al., 1998), however the actual process of planning and implementation has not been documented. The participants for this study were an accomplished physical education teacher, an experienced second-grade classroom teacher, and 35 students from two second-grade classes. Two planning sessions were audio taped. Eight integrated lessons taught by the physical education teacher and three integrated lessons taught by the classroom teacher were video taped. Each teacher was interviewed about the planning and implementation of the unit. The audiotapes and videotapes were transcribed and sent to the teachers for individual member checking. All qualitative data were analyzed using the constant comparison technique to identify categories and themes that were then compared and contrasted among investigators to confirm the findings. The findings indicated that the physical education teacher initiated the collaboration and both teachers shared leadership roles throughout the planning process. They identified and agreed on the focus of the unit in which locomotor skills and concepts were integrated with units of measurement concepts and skills. Building on each other’s ideas, they shaped and edited each lesson’s focus, scope, sequence, and teaching strategies based on the students’ knowledge and skills in both subjects. During the lesson, the physical education teacher and classroom teacher shared the teaching. The physical education teacher taught the integrated movement content and the classroom teacher helped the students make graphs and write in their journals. The teachers attributed their effective collaboration to their prior collaborative working experiences, good personal relationship, common teaching philosophy, enthusiasm about trying out new ideas, mutual respect and trust, and values about the role of other subject areas in enriching and enhancing students learning. The study identified characteristics that contribute to effective planning and implementation and supported the initiation of collaborative interdisciplinary units between physical education and classroom teachers. This study suggested that the interdisciplinary planning and teaching process resulted in a win-win outcome for both teachers.