The purpose of this report is to explore the content-related validity evidence supporting the mathematics components of the "ETS"® National Observational Teaching Exam (NOTE) assessment series, a kindergarten through 6th grade teacher licensure assessment. To establish the content knowledge required for the effective teaching of mathematics in elementary school, we (a) identified content knowledge categories through the use of an expert panel and (b) surveyed a sample of 290 educators to verify that this body of content knowledge is indeed necessary and reasonable for the effective practice of beginning elementary school teachers teaching mathematics. We report information regarding the importance and relevance of mathematics content knowledge areas for both elementary school teachers and faculty members who prepare elementary school teachers. Implications of this work for the mathematics components of the NOTE assessment are discussed. High-Leverage Mathematical Content Areas and Practices are appended. [Some of the content in this report is used in a companion report, "Investigating the Relevance and Importance of English Language Arts Content Knowledge Areas for Beginning Elementary School Teachers. Research Memorandum No. RM-16-08" (ED570638).]