This article provides robust empirical evidence for the association between science teachers' pedagogical content knowledge (PCK) and student achievement. Unlike previous studies, we employed two approaches (text-based vs. video-based tests) to assess if, and to what extent, teachers' PCK assessed by these two approaches are related to student achievement. An analysis utilizing two-level hierarchical linear modeling revealed that PCK assessed by both types of tests reveals a significant and positive association with student achievement. Teachers' PCK assessed by the video-based test better predicted student achievement than teachers' PCK assessed by the text-based test. Based on this result, we discuss implications for research on teacher knowledge and policy implications for teacher education.