A well-designed assessment construct is critical for improving all aspects of quality education and validating the achievement of educational reform. The global prevalence of how teachers communicate learning intentions (LIs) and success criteria (SC) has been of great concern, particularly in the South African context. This study investigates how Meaning Equivalence Reusable Learning Objects (MERLO) pedagogy effectively transforms Senior Phase mathematics teachers' daily practice in the classroom. The study adopted qualitative participatory action research to frame the evolution of teachers' praxeologies such as teachers' meta-didactical and didactical praxeologies, to improve teachers' beliefs and practices to integrate MERLO pedagogy as assessment activities. Twelve Senior Phase teachers were purposively selected in Gauteng, South Africa. The methods used for data generation were interviews, classroom observation, document analysis, field notes and training sessions. Thematic analysis was used to obtain insight into teachers' beliefs and practice of effectively communicating LIs and SC in the classroom. At the initial stage, teachers were examined with regard to their beliefs and practices of assessment practices in the classroom, which informed MERLO intervention. In the second stage, teachers were asked to learn about MERLO items by reading the MERLO handout provided to them, participating in the workshop and sharing their opinions and views with others. In the third stage, teachers had to design MERLO assessment items on their own to assess learners' level of understanding of the mathematical concepts in Senior Phase. The findings revealed that the participating teachers acquired adequate knowledge and skills on MERLO techniques that allowed them to structure and integrate the lesson plan of assessment activities into their mathematics classrooms. This study contributes to the body of knowledge by introducing MERLO pedagogy to Senior Phase South African mathematical teachers as an assessment strategy. COVID-19 caused some teachers to drop out of the study after the pre-MERLO participation phase and, accordingly, future research suggests that more teachers be included in similar studies.