Using a critical race theoretical lens, we examine how South African secondary mathematics teachers of Black students characterised their preparation in the post-apartheid era, how they portrayed good mathematics instruction, and what challenges they identified as barriers to becoming a good mathematics instructor. We found that teachers characterised their preparation in terms of their students' achievement, often talked about the importance of teaching their students mathematical skills and procedures, identified challenges associated with using English as the language of instruction, and engaged in student blaming. Implications from this study include prioritising quality professional development for mathematics teachers of Black students that focuses on developing teachers specialised mathematical knowledge. Professional development should also strengthen South African mathematics teachers' abilities to teach the mathematics register in English and support teachers to examine the detrimental effects of student blaming.