2.3. Data gathering instrument
The “Self-Description Questionnaire-I" developed by Marsh (1992) and adapted into Turkish by Yildiz and Fer(2008) was used for measuring the mathematics self-concept of students in collection of the quantitative data for the study. The Likert-type scale contains total of 8 items. It is designed as a 5-point likert scale with response categories of: Never (1), Rarely (2), Sometimes (3), Usually (4), Always (5). The researcher calculated the Cronbach’s alpha reliability coefficient of the scale as 0.94. The Cronbach alpha coefficient of the scale for this study was 0.84.