Purpose: Understanding the contribution of the use of proper language to thinking development and learning processes, served as the basis of this study. The purpose of this study is to learn from parents, teachers and teacher-trainees whether their view of efficient teaching also relies on the teacher's use of proper language. Design/methodology/approach: In total, 308 teacher-trainees, teachers and parents participated in this mixed-method study. Completing a questionnaire with open and closed questions, they were asked to rate a teacher's professionalism via a written reflection, thereby gauging their perspectives in regard to important teacher characteristics. Findings: The main finding was that teachers' intercultural knowledge and understanding of their students' diversity were perceived as significantly more important than their language register. Participants did not argue that language was not important, but did not necessarily refer to it while assessing the teacher's professionalism. No significant differences were found between the chosen three groups of participants. Research limitations/implications: Although this study included a large number of participants, it is the first of its type. As far as is known, no other study has been published in regard to people evaluating teachers' professionalism on the basis of their language level as expressed in written reflections. Originality/value: From previous studies, it is taken for granted that people will evaluate teachers' professionalism according to the language they use. Nevertheless, this study presents different perspectives that might allow the development of different and teaching and assessments methods.