A case study of a student teacher shows that even under conditions of perceived and/or real constraints on their autonomy, teachers retain great power to shape enacted curriculum (defined as the outcome of interactions among teachers, students, and materials). A student teacher (Ken) was assigned to teach 12th-grade U.S. history in a New York City high school, which had a highly structured curriculum and prescribed policies in instructional arrangements. The student teacher's views of proper curriculum content and appropriate instructional procedures did not always coincide with school policies and the preferences of his cooperating teacher. Yet, even in the earlier stages of his student teaching, while adhering fairly strictly to the required developmental lesson format, Ken was able to weave in material from other lessons thus providing for a coherent sequencing of subject matter. His own voice came through in the sincerity and respect shown to students in his responses to their questions. In the final weeks of his student teaching experience he used other formats successfully, such as small group instruction and role play. This student teacher was more successful in putting his own mark on the curriculum and instructional strategy than he gave himself credit for. This case study suggests that teachers may be wholly or partly oblivious to their own successes. Ken's persistent refrain that he was not free to teach what and how he wanted was truer in his mind than in the classroom. Such a belief can act to disempower teachers, as it did Ken. The study illustrates that even when prescriptive policies on curriculum and instruction are in place, teachers retain room for maneuver, whether they fully appreciate it or not. (Contains 13 references.) (ND)