South African mathematical teachers are being introduced to the pedagogical tool, Meaning Equivalence Reusable Learning Objects (MERLO) as formative assessment (FA) practised in the senior phase (Grade 8 and 9), to promote and support teachers’ professional growth in using FA practices in the classroom. Cultural-historical activity theory (CHAT) and meta-didactical transposition (MDT) was used to frame the evolution process of teachers’ praxeologies. This study used qualitative participatory action research that encompassed three phases: pre-MERLO participation, MERLO participation and post-MERLO participation phase. The study was conducted in the northeast of Pretoria in Tshwane district in the province of Gauteng. Twelve senior phase mathematics teachers were purposively sampled in six public schools before workshop training. During workshop training, only five teachers participated due to the COVID-19 outbreak. The data collection instrument in my study used pre-and post-interviews, classroom observations, field notes, teachers’ reflective journals, teachers’ lesson plans learners’ workbooks and learners’ worksheets. From the subsequent MERLO participation, the findings revealed that the participating teachers acquired adequate knowledge and skills of meta-didactical praxeologies that allowed them to structure and integrate the lesson plan of teachers’ didactical praxeologies as FA activities into their mathematics classrooms. Furthermore, the teachers revealed that the learners showed more interest and motivation in the lesson. The learners were also actively involved in the lesson, developed a deeper understanding of mathematics content, and showed increased autonomy in learning. This study contributes to introducing the dynamic evolution of teachers’ praxeology of meta-didactical praxeologies and didactical praxeologies to South African mathematics teachers in the senior phase (Grade 8 and 9), in which the teachers used the pedagogical tool MERLO to support FA activities in the mathematics classroom. However, it is important to note that the effectiveness of MERLO participation training processes used in my study is ongoing research with a current focus on teachers’ professional development, with a future view on implementing the pedagogical tool MERLO in South African schools. In addition, the effectiveness of the training could also be used to empower other teachers globally. / Thesis (PhD (Assessment and Quality Assurance))--University of Pretoria, 2021. / UP doctoral research bursary / Science, Mathematics and Technology Education / PhD (Assessment and Quality Assurance) / Restricted