Implementation fidelity and its impact on the success of intervention programmes: The case of two mental starters projects

Background: In response to persistent challenges in early grade mathematics achievement in South Africa, two intervention projects – Base-Ten Thinking (BTT) and the Mental Starters Assessment Project (MSAP) – were implemented to enhance number sense through mental mathematics in Grades 2 and 3. These projects integrate Freudenthal’s theory of number structuring with context-specific mental strategies, namely Jump and Bridging-through-ten. Aim: To examine how the fidelity of implementation of mental mathematics interventions influences learner performance in early grade classrooms. Setting: The study was conducted in four South African primary schools participating in the BTT and MSAP interventions, each reflecting varying levels of fidelity (high to no fidelity) to the instructional model. Methods: A design research approach was adopted, using 15 video-recorded lessons and pre- and post-test data from 155 learners taught by five teachers. Implementation fidelity was assessed using descriptors derived from components of Lemire et al.’s framework for conceptualising implementation fidelity. Both quantitative and qualitative analyses were employed. Results: Schools with high fidelity demonstrated statistically significant gains, particularly in jump strategy tasks, compared to schools with moderate, low or no fidelity. This contrasts with earlier findings where moderate fidelity, which allows for teacher agency, yielded better outcomes. The study highlights the value of structured instructional coherence. Conclusion: The study underscores the importance of well-structured, evidence-based and well-researched intervention models targeted towards addressing foundational gaps in mathematics in early grade classrooms. Contribution: In addition to the contribution on the importance of well-structured and thoroughly researched instructional models, the study also makes a methodological contribution by providing an analytical framework linking fidelity, professional development and early grade mathematics instruction.