School mathematics textbooks are used in varying ways and to varying degrees by teachers and schools. The textbook materials of focus in this study were designed in accordance with current curriculum reform principles, advocating a student-centred approach that emphasises conceptual understanding and fostering of students' thinking and mathematical communication. The purpose of this study was to investigate the impact of a new reform-based mathematics textbooks series on teachers' classroom practices. Observations were conducted in six elementary teachers' mathematics classrooms as they implemented the new textbook series. The observations were combined with interview data to explore the impact of the textbook upon teachers' classroom practice. Through combining interview data with classroom observations, this study provided a snapshot of various teachers' use of new curriculum materials. It was apparent from this study that the materials were used to varying degrees of effectiveness by individual teachers. Results suggested that when the textbook was regarded as a resource, quality pedagogy was enacted. Conversely, if teachers felt challenged by the new reforms evidenced in the textbook they tended to follow the textbook in a prescriptive manner, resulting in teacher-directed pedagogy.