Interdisciplinary science teaching is a challenge for German teachers due to primarily subject-specific teacher education in biology, chemistry, and physics. Content knowledge is an important aspect of professional competence in teacher education. We address the self-rating of content knowledge in a study on developing a suitable measure. Previous measures of self-rated content knowledge in science are general, focus on primary education, or do not integrate the core ideas of curricula for lower secondary German education. Therefore, we developed and validated a new discipline-specific measure.
Confirmatory factor analysis (n = 552) established that biology, chemistry, and physics are factors of self-rated content knowledge and indicated that self-rated content knowledge in science is subject-specific. The correlation between self-rated content knowledge and academic self-concept in science, and the impact of science education subjects studied and the final science grades in secondary school on self-rated content knowledge in science support the validity of the new measure and its disciplinarity. Concluding from the findings of this valid and reliable measure, the different factors of self-rated content knowledge in science make interdisciplinary science teaching difficult. This conclusion underlines the need for qualification in interdisciplinary science teaching.