Nine hundred seventy-five 6th grade (12-year old) and 639 9th-grade (15-year old) Turkish adolescent students from, respectively 12 middle and 6 high schools located in the metropolitan area of Istanbul, Turkey, participated at T1 (October of 2014); among them 425 (73.8% 6-the graders) participated also at T2, five months later. Data were collected during one-hour class-session. After getting consent from the Ministry of Education, the school principals and parents, a research assistant explained the purpose of the study and assured students that their participation would be anonymous and voluntary. An unexpected administrative problem (the page that contained questions on demographics was omitted), prevented us from getting information about the gender and the precise age of participants, but as school principals informed us in retrospect, the distribution of gender in the classes that we sampled was approximately equal. The questionnaires were translated and back-translated by two experts and adjusted according to the procedures proposed by Hambleton (1994). A 5-point Likert-type scale (1 = strongly disagree; 5 = strongly agree) was used in all the measures.