This paper is a report of a study into the impact of a professional development programme designed to bring about changes in the classroom practices of teachers and change in their beliefs and attitudes. The programme is offered to in-service teachers of mathematics over a period of two years. The study is focussed on the assumption that what a teacher believes about mathematics and teaching mathematics is integrally related to the quality of mathematics being taught in the classroom (Thompson, 1992). In addition, the attitudes to mathematics itself may affect the teacher’s attitudes to the teaching of mathematics, which in turn have a powerful impact on the atmosphere and ethos of the mathematics classroom (Ernest, 1989). Also notable is the importance ascribed to the teacher’s reflectivity concerning the teaching and learning of mathematics and implementation of change in the classroom.