Like their students, teachers may hold a variety of naive conceptions that have been hypothesized to limit their ability to support students' learning. This study examines whether changes in elementary students' conceptions are related to their teachers' content knowledge, attitudes, and understanding of conceptual change. The study takes place in the context of the adoption of a new unit on seasonal change in which students build and use sundials to observe seasonal differences in the apparent motion of the Sun across the sky. A mixed-method approach is used. Data sources include pre- and post-tests for students and teacher interviews and questionnaires. Results indicate that changes in students' conceptions may be related to their teachers' knowledge of the content, attitudes toward science, and understanding of conceptual change. One teacher had low attitude toward science and limited knowledge of conceptual change. After instruction, her students' responses became less accurate but more homogeneous than before instruction. The other teacher had high attitude and moderate knowledge of conceptual change. Her students showed gains from pre- to post-test, including responses that were more scientifically accurate than the teachers' initial answers.