This article presents Hofer’s (1981, 1986) research about students’ categories in teachers’ cognition. Its aim is to extract Hofers’ methodology and to supply it with approaches used by researchers interested in the categorization of persons or objects (Sternberg, 2007; Reed, 2011). Nine Geneva elementary school female teachers took part in this research that pursue two goals: (a) verifying the relevance of a statistical method (cluster analysis) to identify students’ categories in teachers’ general pedagogical knowledge, and (b) confirm whether or not the central-peripheral internal structure of the conclusions Hofer thought he was demonstrating is the result of his statistical algorithms. Results are discussed in terms of methodological and empirical perspectives.