This paper reports on results of research from a 25-year program of studies investigating teacher-student relationships in secondary classrooms. The authors review the research that examines teaching from an interpersonal perspective using a communicative systems approach and propose a model to describe teacher-student relationships in terms of teacher behavior. The studies used the Questionnaire on Teacher Interaction (QTI) to collect data on students' and teachers' perceptions of the teacher-student relationship. The authors review studies showing that teacher-student relationships appropriate for high student outcomes are characterized by a rather high degree of teacher influence and proximity towards students. Studies on non-verbal behavior and the spatial position of the teacher in the class support the need for beginning teachers to portray the image of an experienced teacher whenever they address the class as a group. The paper concludes that the QTI is a useful research tool, but research on the QTI as a feedback instrument for teachers is insufficient to prove its usefulness. [For Chapter 2, see EJ739718.]