This dissertation examined the emotional and relational aspects of co-design, and how the co-design process for creating caring classrooms supported teacher learning. I drew on key elements of improvement science, as a type of design-based implementation research, to understand teachers as learners and as experts. I elaborated two layers of theory to guide this study. First, I conceptualized caring in the context of intentional relationship building with students, described characteristics of caring classrooms, and identified dilemmas that arise from caring. Then, I explored expansive learning and deliberative agency as concepts for understanding teacher learning. With a small group of teachers, we planned, implemented, studied, and revised the routine designed for improving relationships with students. We created a student survey to learn about students' experiences and used data to guide revisions. Through qualitative data collection and analysis, I tested, revised, and refined my high-level conjecture that the co-design process supported teacher learning. The findings suggest teachers had opportunities to demonstrate deliberative agency, learn, and grow professionally. I described the evolution of the design and examined the ways the design team grappled with dilemmas. Teachers engaged in learning as they broke away from old routines to design and implement a new routine in their classrooms. I also examined teachers' talk when looking at data and found that in analyzing student data together, talk turned both towards and away from deeper investigations of pedagogical practice and the practical measure. Teachers considered students' experiences and feelings within their classrooms, which made the data more salient and contributed to the emotional dimensions of design work. In a case study of one teacher, I found that she grappled with dilemmas connected to the co-design process and caring for students, and she used the design team space to reflect on dilemmas and explore emotions related to the dilemmas. Through this study I show how improving teacher-student relationships requires risk-taking, creating classrooms can be complex, and the design team space can become a site of care.