The purpose of this research was to measure teachers and students interpersonal competences in situations that a teacher may face at school and which require interpersonal interaction with students, parents or other teachers. In addition, the mediating role of interpersonal competences was examined in the relationship between teachers' interpersonal style and burnout. In order to measure interpersonal competences, a test (Teachers' Interpersonal Competency Test) was constructed according to the standards of Situational Judgement Tests (SJTs). The sample consisted of 269 Greek General and Special Education teachers and 117 students from General and Special Education Departments. Participants completed the Teachers' Interpersonal Competency Test, the Questionnaire on Teacher Interaction and the Maslach Burnout Inventory. According to the results of the statistical analysis, interpersonal competences were mainly differentiated between teachers who worked at different levels of education. Differences in interpersonal competences also occurred between teachers and students, as well as between first- and third-year students. Interpersonal competences have been shown to play a protective mediating role between interpersonal style and burnout. The present research contributes to the study of teachers' interpersonal competences and their importance to the wellbeing of teachers and students as well, through the development of supportive interpersonal styles.