In this descriptive study, the science subject matter knowledge of preservice and inservice elementary teachers was examined and compared. Over an eight-year period, answers to 13 science questions, including 10 from the US National Science Foundation's Survey of Public Attitudes Toward and Understanding of Science and Technology, were collected from a total of 414 preservice and 67 inservice teachers during first-day discussions in elementary science methods courses. Both groups outperformed average citizens on the 10 survey questions. However, three other questions used to introduce discussion of why students may find learning science difficult revealed lack of conceptual understanding of basic physical and biological phenomena commonly found in most elementary science curricula. Results and implications are discussed in the context of increasing expectations for subject matter competence demanded of 'highly qualified teachers' under provisions of the 2001 US Elementary and Secondary Education Act ('No Child Left Behind Act').