Planning is an important phase of teaching, during which teachers make decisions about various aspects of instruction that ultimately shape students’ opportunities to learn. Prior research on teacher planning, however, fails to adequately describe experienced teachers’ planning decisions, and is unclear about the extent to which teachers use curriculum materials to inform their decisions. Using data from 6th grade mathematics teachers’ use of curriculum materials, this study presents a discipline-specific model of experienced mathematics teachers’ planning. The proposed model provides a lens for understanding the nature of teachers’ planning decisions, and the conditions under which such decisions change over time.