Why is secondary mathematics difficult to learn? Perspectives from in-service teachers and cognitive load theory

Background: Secondary mathematics learning presents significant difficulties for many students, yet the sources of this complexity remain inadequately understood. Objective: This study investigates complexity sources in secondary mathematics by examining the relationship between in-service teachers’ perspectives and cognitive load theory’s concept of element interactivity. Methods: Semi-structured interviews were conducted with experienced secondary mathematics teachers (N = 11), analysing their perceptions of learning difficulties in fraction operations, focusing on both theoretical content and problem-solving tasks. Results: Complexity arises from multiple sources, which were defined and classified into knowledge complexity (intrinsic to mathematics) and task complexity (related to instructional design). Conclusions: The study bridges theoretical frameworks with classroom experience, providing evidence that element interactivity explains teachers’ observations of mathematical learning difficulties. The identified sources of complexity form a taxonomy that can potentially be used for achieving more precise and holistic measurements of element interactivity.