In Belize, the percentage of untrained teachers (i.e. teachers with the equivalent of a high school education or less) is one of the highest in the region of Latin America and the Caribbean. In response to growing student cohorts, the increased demand for more classroom teachers has led to significant decrease in the proportion of trained teachers at both the primary and secondary levels. Fewer than 45% of teachers at primary and secondary levels are trained, whereas some countries in the region report more than 80% are trained. Perhaps as a result of the lack of training, a content test that was applied to a representative sample of teachers nationwide as part of this study design revealed important gaps in teachers' math content knowledge. The authors hypothesized that increased math content and pedagogical skill enhancement of teachers would lead to improved student outcomes on content knowledge in mathematics. The Teacher-Led Math Inquiry (TLMI) project posed three research questions: 1.When controlling for pretest differences, do students exposed to the TLMI treatment exhibit higher post-treatment math achievement than students in the control group at the end of one school year? (Intent to treat model); 2. To what extent does implementation fidelity as an added variable in the ITT model moderate post-treatment math achievement? (Test of treatment model); and 3. How did teachers view implementation of the TLMI approach? (Qualitative results). The present study indicates TLMI has a substantive significant positive effect on student math performance in comparison to traditional instructional practices in Belize, specifically in the Belize District. Tables are appended.