In their examination of elementary science classrooms, Amerine and Bilmes (1988) found that following instructions requires students to understand the relationship between the projected outcome and the corresponding course of actions. One of the most important resources for instructions is the lesson plan, which prescribes the sequence of teaching. However, there is often a gap between what is planned and what actually happens in the classroom. This raises the question of how teachers come to terms with contingent variants and unexpected outcomes that real-time interactions occasion and how lesson plans are configured into these processes. This study examines a teacher education program that uses lesson plans as a central resource for teaching mathematics. The results suggest that classroom teachers use lesson plans as communicative resources to identify problems, specify assumptions about their teaching and act on the evolving contingency of classroom interaction. The interactional contingency is the locus of teaching practices, not an obstacle to the application of procedures in lesson plans.