A key responsibility of teaching to help students develop understanding and skill in academic content. Content knowledge for teaching (CKT) involves being able to unpack proficient knowledge in ways that make it explicit. The specialized ways of knowing needed for teaching are not intuitive and are often at odds with the “obviousness” that accompanies fluent expertise or individual academic success. Assessments of teachers’ content knowledge, however, often only appraise academic understanding and skill and do not tap the degree to which teachers are able to make the tacit explicit and the procedural understandable. This project seeks to address this gap by building tasks and items to assess the specialized content knowledge entailed by the work of teaching secondary English language arts (ELA) and mathematics. This kind of content knowledge is one important component of a practice-focused curriculum for preparing teachers and for the assessment of candidates’ readiness for responsible independent practice. We will develop, pilot test, and conduct validation studies of two sets of tasks and items of content knowledge for teaching middle and high school, one for English language arts and the other for mathematics.