Integrating psychological theories and educational practice has long been the aim of educational psychologists. This paper presents an overview of the results of a three-step research project, Students' Socio-moral and Interpersonal Development. Initial basic research traced the developmental patterns of the students' interpersonal competence in solving communicative conflicts with their classmates and teachers. The second stage of the project consisted of a prevention and intervention programme at school, as teachers were guided in working constructively with their students on socio-moral and interpersonal issues. During these intervention programmes applied research was conducted, focussing on the students' developmental progress in interpersonal understanding and actions as a function of their participation. Finally, teachers' own professional development was traced during the course of their work with students in this area. As the teacher is a "key person" in promoting social learning, this presentation focuses on this third stage of the research.