The teaching practices of mathematics are still little-known in Rwandan schools though the Competence-Based Curriculum (CBC) and many pedagogical documents recommend how to assess, what to assess, and when to assess the effective teaching of mathematics. This study aimed to assess Rwandan mathematics teachers' practices through pedagogical content knowledge (PCK). We sampled 14 mathematics teachers having similar educational backgrounds. Seven of them were sampled from Teacher Training Colleges (TTC), and the other seven were non-TTC teachers (selected from general secondary schools). We adopted a pedagogic approach to analyze the assessment practices and the tasks proposed by teachers to students. We also analyzed 35 items related to pedagogical content knowledge for teaching (PCK) among these two groups of teachers. Although the results about differences between two groups of seven teachers were not considered robust differences, it was still revealed that in all item categories related to PCK, TTC teachers have less performance than non-TTC teachers. The lack of mastery of content and specialized knowledge at the university level was found to cause this. We also found challenges related to teachers' assessment skills, especially mathematical complexity, as indicated by the interview results. We, therefore, recommend that all teachers, especially TTC teachers, be offered training in content knowledge so that they strengthen their teaching practices.