Purpose: Although high-quality comparative data from international assessments are now more widely available, to what extent is that data being used to trigger, inform, and direct educational change in non-Organization for Economic Co-Operation and Development (OECD) countries? The purpose of this paper is to develop a theoretical framework to guide a case analysis of Trinidad and Tobago's system response to international assessment data. Design/methodology/approach: This is a single-nation explanatory case study using data from policy documents and elite interviews. Findings are generated through inductive thematic analysis. Findings: The four emerging themes were: first, weaknesses in the national evaluation system; second, policy-making practices not attuned to data; third, lack of collaboration and stakeholder involvement; and fourth, challenges in accessing and using data. Findings suggested that data rarely acted alone to trigger system change. Critical to initiating and sustaining effective data use for system reform were policy-making contexts and mental maps of system leaders, which in this context acted as barriers. Respondents believed that greater strategic leadership from politicians and technocrats could ensure data-informed systemic change. Research limitations/implications: The study focuses upon data use and data-driven decision making for whole system reform within a single country context. However, it advances theory that might be applied to other non-OECD cases. Originality/value: The findings contribute to the refinement of a conceptual model explaining data-driven system reform applicable to non-OECD contexts. The role of system leaders when using international assessment data is clarified.