Despite the importance of developing elementary science teachers' content knowledge for teaching (CKT), there are limited assessments that have been designed to measure the full breadth of their CKT at scale. Our overall researchassessments, content knowledge for teaching, elementary science, matter and its interactions, pedagogical content knowledge High-quality science instruction requires that science teachers leverage their content knowledge for teaching (CKT) in the work of teaching (National Research Council, 2012; NGSS Lead States, 2013). CKT refers to the professional knowledge that teachers draw upon as they engage in the work of teaching in a specific discipline (Loewenberg Ball et al., 2008). The main focus here is on the application-or use-of their knowledge in the actual tasks of teachingfor example, the knowledge that teachers use when they prepare for, enact, and reflect on their instruction with students. CKT includes both subject matter knowledge, as well as other forms of practice-based knowledge that are directly tied to the work of teaching-what is commonly referred to as teachers' specialized and pedagogical content knowledge. In the area of science this includes knowledge about how students think about, engage in, and learn about specific scientific practices and concepts, as well as knowledge about various instructional strategies and tools science teachers can draw upon to develop students' learning (Carlson et al., 2019;Mikeska et al., 2020;Schneider & Plasman, 2011).In science education, research has indicated that CKT, particularly science teachers' pedagogical content knowledge, can be quite nuanced and variable across subjects, topics, concepts, and even knowledge components (e.g., knowledge of student ideas vs. knowledge of instructional strategies) (
