This study explores new directions to study and combine measurements of instructional expertise and teachers’ interpersonal relationships with students. The sample comprises 34 in-service teachers. The My Teacher questionnaire (MTQ) was used to operationalize teachers’ instructional expertise. The Questionnaire of Teacher Interaction (QTI) was used to describe teachers’ interpersonal relationships with students. Hypotheses were tested using circular mixed-effects models. Results indicate that teachers’ interpersonal relationships differ at successive levels of instructional expertise. Results further indicated that increases in instructional expertise are associated with a sharp decrease in the within-class variance in interpersonal relationships. Specifically, the higher teachers’ instructional expertise, the more teachers' interpersonal relationships are described as “directing” and “helpful” by all students in the class.