The purpose of this report is to examine the performance of assessment items designed to measure elementary teachers' content knowledge for teaching (CKT) science as part of the ETS Educator Series. The Elementary Education: CKT Science assessment is 1 component of licensure examination through the PRAXIS assessments. The Elementary Education: CKT Science assessment is designed to determine whether kindergarten through 6th‐grade elementary teacher candidates have the essential content knowledge needed for teaching elementary science as new teachers at the entry level. This report provides information about the development of the Elementary Education: CKT Science framework and the associated assessment items. The main part of the report focuses on the evidence gathered when piloting 104 CKT science assessment items with 417 preservice and novice elementary teachers. This evidence included the following: (a) how these new CKT science assessment items function, including their item difficulties and discrimination, and reliabilities of the pilot forms and of the classification of examinees; (b) how teachers perceive the importance and relevance of these new assessment items; (c) how teachers' performances on these items relate to their background characteristics and professional and academic preparation; and (d) how teachers' performances on the CKT science items compare to their performances on an assessment designed to measure only their science subject matter knowledge.