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.