„Instructional quality depends on teachers’ content knowledge (a thorough understanding of the subject matter), pedagogical content knowledge (a solid grasp of teaching methods), and pedagogical knowledge (knowledge of educational psychology), which, in turn, are positively related to teachers’ formal qualifications.“
Dr. Karin Guill u. a., Assessing the instructional quality of private tutoring and its effects on student outcomes. In: British Journal of Educational Psychology (2020), 90, S. 285.