The purpose of this qualitative descriptive study was to explore how heads of department support the professional development of mathematics teachers in public secondary schools to improve learner performance in Mathematics. Mathematics occupies a central role in future innovation and serves as a basic subject for many other disciplines. Teachers, too, require relevant education and development to be adequately prepared to handle and manage the teaching-learning tasks they are expected to carry out in Mathematics. While there is consensus about poor performance by matriculants in their Mathematics examination, the details of strategies and means to improve performance in Mathematics through professional teacher development remains under-researched. In this study, a qualitative case study design was used to investigate the professional development of teachers within a real-life context to gather comprehensive, systematic and in-depth information about the phenomenon, using semi-structured interviews. A total of eight participants, 2 mathematics HoDs and 6 mathematics teachers from two secondary schools in the Tshwane South District of Gauteng Province were selected, using purposive sampling. The research questions were concerned with understanding the concept, professional development; the HoDs’ and Mathematics teachers’ experiences of professional development; and the challenges experienced, and strategies used, by HoDs to develop the Mathematics teachers. The collected data was transcribed, categorized and presented as themes with direct quotations from the participants to support the themes. The findings of this study show that the two HoDs perceive profession development as workshops and training programmes initiated and conducted by the Department of Education and not as their direct responsibility. There was no evidence of school-based professional development programmes. The challenges that they experienced included the teachers’ reluctance concerning, and resistance to, professional development. They recognized team work and peer support as effective strategies for developing Mathematics teachers.