There is a widespread belief among both teachers and students that mathematics, like any other factual subject, needs to be learnt. Traditionally the major emphasis in the mathematics classroom has been to teach students the processes of an algorithm and to drill them in these processes. This study investigates the influence of mentoring on teachers' understanding of what mathematics is, how it is learnt and how teachers' actions can make learning more meaningful for students. The sample for the study were two teachers from the primary and secondary sections of a school. Data sources were notes of lesson observations, reflective journals, verbatim transcripts of conferences and semi-structured interviews. The data was analyzed as two separate case studies. The study found that mentoring did influence teachers' practices and beliefs and showed that the two are interrelated. It found that mentoring can encourage teachers to reflect on their own practice and in a supportive and non-threatening environment changes will be attempted. The teachers evaluated the new learning in the light of student outcomes. The study found that teacher development is an on-going, individual and highly personal process and teachers have varying learning styles. Willingness and ability to change must take into account the culture and organizational structure of the school. Cultures which encourage collaboration and empower teachers to make decisions provide an environment where teachers are more reflective about their actions and are more willing to share new learning with others. Hierarchical organizations hinder change for teachers feel compelled to follow directives and live up to the expectations of those in authority. The study also found that, whatever the subject matter, the moral dimensions of teaching cannot be ignored.