This paper aims to provide an understanding of effective professional development (PD) for mathematics teachers according to the context of South Sudan schools. Hunsicker’s (2011) checklist of effective PD was taken as a framework. The framework has five characteristics—supportive, job-embedded, instructional focused, collaborative, and ongoing—and these five characteristics have been used for shaping the study. Interviews were designed and administered to educational officials, principals of two schools, and six sampled mathematics teachers, patterning their understanding about effective PD of mathematics teachers in the South Sudan school context. The analysis showed that the types of PD that exist in the South Sudan school context include the preparation of a lesson plan and the scheme of work for novice teachers, a weekly professional participation of teachers within their working hours, and informal dialog and guidance among peers. In addition, some unqualified teachers are sent to teacher training institutions during holiday times, which can be regarded as a kind of in-service and continuous PD. Our findings are that most of the participants do not have a clear view of what effective PD means. The participants mentioned aspects that can be seen as parts of effective PD according to the literature, but none of them had a holistic or explicit understanding. There is a need to engage those stakeholders to work deeply on aspects of effective PD if a meaningful improvement in student learning is to happen in classrooms.