Science as inquiry is a key content standard in the National Science Education Standards; however, few secondary science teachers successfully and consistently implement inquiry-based instruction in their classrooms. This research examines the role of reform-based curricular materials in influencing the classroom practices of 12 high school chemistry teachers and investigates the role of the teachers' knowledge and beliefs in their implementation of the reform-based chemistry curriculum. Qualitative and quantitative data were collected in the form of beliefs interviews and classroom observations. The teachers' classroom practices were measured prior to and during the field test of the reform-based chemistry curriculum. Analysis of the data revealed that teachers' classroom practice became more reform-based in the presence of the new curriculum; however, the degree of change is related to the teachers' beliefs about teaching and learning, depth of chemistry knowledge, and years of teaching experience. Experienced, out-of-discipline teachers with transitional or student-centered teaching beliefs demonstrated the most growth in reform-based teaching practices. This study reinforces the need for reform-based curriculum to assist teachers in implementing the intent of the National Science Education Standards.