This study examines the validity of the Force Concept Inventory (FCI) in Ugandan secondary schools using Item Response Curves (IRCs) and provides a comparative evaluation of its effectiveness across different educational contexts. The survey focused on Senior Four students preparing for the Uganda Certificate of Education (UCE) examinations, with a representative sample of 941 students (aged 15–17) selected through a multi-stage sampling technique. The initial analysis employed Classical Test Theory (CTT) metrics before the detailed analysis of IRCs for the FCI items. The CTT evaluates item-level and whole test statistics like item difficulty level, discrimination index, and reliability. The CTT indices revealed that the FCI was highly challenging, with an average score of 5.76 out of 30 and a low-reliability coefficient (α = 0.15). Additionally, 73.3% of the items showed poor discrimination, and some distractors were ineffective. The detailed analysis of IRCs showed that several FCI items are inefficient in the context of the Ugandan education system. The IRCs also demonstrated a widespread choice of distractors for many items, with overall scores falling below the threshold indicative of a generally agreed-upon understanding of Newtonian physics. Comparative analysis from other global contexts studies suggests that language barriers, curriculum differences, and instructional methods influence student performance. These findings underscore the necessity of adapting the FCI tool to better fit local educational contexts and implementing additional instructional strategies to enhance conceptual understanding. A more culturally and contextually adapted diagnostic tool may improve physics education and better assess students’ conceptual comprehension of force and motion within the region.