The Evolution of Specialised Content Knowledge in Subtraction: Evidence From a Pre-Service Teacher Case Study

This instrumental case study analyses the evolution of the specialised knowledge and affective domain of a pre-service primary education teacher regarding the subtraction algorithm. Traditionally, subtraction with regrouping is taught via procedural metaphors which often cause mathematical misconceptions. To address this problem, an instructional intervention based on the Mathematics Teacher’s Specialised Knowledge (MTSK) framework was implemented to examine changes in both specialised knowledge and the affective domain. This instrumental qualitative case study adopted an interpretative approach. Data were analysed using deductive-inductive content analysis based on audiovisual teaching tasks, questionnaires, and a semi-structured interview. Findings suggest substantial changes: cognitively, the pre-service teacher shifted from relying on mechanical rules to demonstrating a structural mastery of the Decimal Numbering System using manipulative tools. Emotionally, acquiring a deep relational understanding allowed her to overcome her academic past and experience true math-redemption. The study concludes that addressing mathematical cognition, pedagogical strategies, and emotional history simultaneously empowers future educators to break the generational cycle of mathematical fear.