General pedagogical knowledge versus pedagogical content knowledge? The structure of professional knowledge in pre-service teachers of German, English, and Mathematics at university

General pedagogical knowledge (GPK) and pedagogical content knowledge (PCK) are central cognitive elements in the professional competence of teachers. Thus initial teacher education aims at the acquisition of this relevant knowledge. However, the question how GPK and PCK are related to each other or can be separated from each other has not yet been answered, neither conceptually nor empirically. Against this background, this article focuses on two research questions on the basis of standardized knowledge tests administered to 889 pre-service teachers of German, English and Mathematics from two large universities: (1) Can GPK empirically be separated from PCK of German, English, and Mathematics? (2) Are there differences in pre-service teachers' PCK test scores depending on their stage of training (Bachelor versus Master) and can PCK test scores additionally be explained by specific learning opportunities in the area of PCK (when compared with GPK test scores)? On the one hand, findings show that GPK and PCK can empirically be separated. This is true for all three domains (construct validity), whereby the correlation between GPK and Mathematics PCK is lower than the correlations between GPK and German PCK and English PCK (when controlled for background and entry characteristics of students and their learning opportunities). On the other hand, a comparison between cohorts of Bachelor and Master student teachers provides evidence that the more advanced Master students outperform the Bachelor students in all knowledge tests (curricular validity). In addition, German PCK and English PCK (better than Mathematics PCK) can be explained by subject-specific learning opportunities (convergent validity) and be demarcated from GPK (discriminant validity). Implications for current initiatives of quality assurance in initial teacher education are discussed.