Due to increased external, societal pressure on schools via developments such as accountability and accreditation, there is a growing need of schools for instruments that provide them with information on the quality of the teaching and learning processes they organize. This paper presents an instrument that can be used to diagnose teachers’ interpersonal skills, one element of teaching quality that may be of interest to schools. The instrument is based on the theory of interpersonal communication of Timothy Leary. Apart from a discussion of the theoretical framework behind the instrument, the paper presents information on the instrument itself and procedures for using the instrument with teachers and students. Also, information is provided on possibilities of using the instrument for staff development and other purposes of schools. The instrument appears to be of high quality and is accompanied by a large database of information linking it to other factors in the classroom context.