“…There is increasing evidence that PCK is related to the quality of classroom instruction (Ball, Lubienski, & Mewborn, ; Baumert et al, ; Kunter, Klusmann, et al, ; Park, Jang, Chen, & Jung, ) and students' learning progress (Alonzo, Kobarg, & Seidel, ; Baumert et al, ; Kunter, Klusmann, et al, ; Lange et al, ; Lange, Kleickmann, Tröbst, & Möller, ; Mansor, Halim, & Osman, ). Nevertheless, despite its recognized vitality for teachers' professional competence, PCK lacks a clear definition.…”