ISSN 2087-8885 E-ISSN 2407-0610 Journal on Mathematics Education Volume 8, No. 2, July 2017, pp. 165-184 DOI: http://dx.doi.org/10.22342/jme.8.2.4102.165-184 UNDERSTANDING OF PROSPECTIVE MATHEMATICS TEACHERS OF THE CONCEPT OF DIAGONAL Ülkü Ayvaz1, Nazan Gündüz1, Figen Bozkuş2 1Abant Izzet Baysal University, 14280 Merkez/Bolu Merkez/Bolu, Turkey 2Kocaeli Universty, Turkey Email:
[email protected] Abstract This study aims to investigate the concept images of prospective mathematics teachers about the concept of diagonal. With this aim, case study method was used in the study. The participants of the study were consisted of 7 prospective teachers educating at the Department of Mathematics Education. Criterion sampling method was used to select the participants and the criterion was determined as taking the course of geometry in the graduate program. Data was collected in two steps: a diagnostic test form about the definition and features of diagonal was applied to participants firstly and according to the answers of the participants to the diagnostic test form, semi-structured interviews were carried out. Data collected form the diagnostic test form and the semi-structured interviews were analyzed with descriptive analysis. According to the results of the study, it is understood that the prospective teachers had difficulties with the diagonals of parallelogram, rhombus and deltoid. Moreover, it is also seen that the prospective teachers were inadequate to support their ideas with further explanations although they could answer correctly. İt is thought that the inadequacy of the prospective teachers stems from the inadequacy related to proof.