Diagnosing Secondary School Students’ Misconceptions in Circular Motion Using Item Response Curves from the Circular Motion Concept Inventory

A significant body of research has employed concept inventories to diagnose students’ conceptual understanding in physics. However, there remains limited evidence on their effectiveness in secondary school contexts in Sub-Saharan Africa and on whether advanced item-level analyses can reveal persistent misconceptions. This study examines the application of the Circular Motion Concept Inventory (CMCI) to evaluate learning progress and identify misconceptions among Ugandan secondary school physics students. Using a pre–post-test design, the CMCI was administered to 198 Advanced Level physics students both before and after a structured instructional intervention that incorporated physical models, diagrams, graphs, charts, and illustrations. Data were analysed using descriptive statistics, Classical Test Theory (CTT), and Item Response Curves (IRCs) to assess normalized learning gain, item-based indices, and misconception patterns across different ability levels. Results indicate a moderate improvement in conceptual understanding, with mean scores increasing from 6.61 on the pre-test to 10.03 on the post-test, and average item difficulty rising to 0.50. Despite these gains, IRCs analyses revealed persistent misconceptions related to centripetal force, acceleration direction, and motion on banked curves, particularly among low-ability students. Think-aloud interviews supported these findings by exposing gaps in students’ conceptual reasoning even when correct answers were selected. The study demonstrates that IRC analysis provides diagnostic insights beyond conventional CTT measures by revealing how misconceptions persist across ability levels. These findings underscore the value of integrating CMCI and IRC-based analyses into instructional design to inform targeted, evidence-based interventions aimed at improving students’ conceptual understanding of circular motion.