ABSTRACT Effective teacher education is expected to ensure that future teachers acquire professional knowledge that is relevant for coping successfully with the requirements of their teaching practice. To strengthen evidence-based teacher education, we need to better understand which teacher education outcomes are predictive for high-quality instruction and student learning. This study hence investigates the impact of teachers’ pedagogical-psychological teaching knowledge (PPTK) on student’s perception of instructional quality and students’ achievement in mathematics. The study is based on longitudinal data of 28 early career primary school teachers and their students (n = 509). The results indicate PPTK as a significant predictor for students’ perception of teachers’ classroom management as well as teachers’ quality of explaining. PPTK and teachers’ cognitive activation as perceived by students are significant predictors for students’ mathematics achievement. These results emphasize the importance of PPTK for successful learning processes in mathematics in primary school. The findings are discussed regarding their relevance for the effectiveness of teacher education.