The purpose of the current study is to determine to what extent the following four variables explain K-8 students' SBS success levels; these variables being attendance to private SBS preperation courses, multidimensional perfectionism, parental attitude types, and test anxiety. SBS is a nationwide, high stake, high school placement test taken by middle school students in the Turkish education system since the 2007-2008 school year. The sample of this study consists of 460 cluster sampled 8th grade students, of which 257 are girls and 203 are boys all from the city center of the province of Tokat, Turkey. The Multi-dimensional Perfectionism Scale (MPS), Parental Attitude Type Scale, Westside Test Anxiety Scale, and a personal information sheet were used to collect data which was then analyzed using hierarchical linear regression, independent group t tests and chi square tests. According to the findings, the most effective variable in determining a student's level of success is attendance to private preperation courses. Other significant predictors of success on the SBS are the espousal of a perfectionist attitude by parents and a student's level of test anxiety. Moreover, the most effective factor influencing SBS scores of students who do not attend preperation courses is his parents' adoption of an authoritarian attitude. While the "Order" dimension of the MPS and "test anxiety" were negative predictors of students' success on the SBS, "responsibility-centered parents' attitude" was positively related to the students' scores. "Doubt from behaviors" was the most effective negative predictor explaining the SBS scores of students who did not attend private SBS preperation courses. The findings of the study suggest that as one's income level increases, so does the duration of time spent attending SBS prep courses, and this increased level of success can also be attributed to effective parent involvement in students' lives. However, family's income stands as a definite medium, explaining students' SBS success. As a result of the current study, SBS preperation courses has been found to be the most defining factor in students' SBS scores. According to the findings, students' success on large scale tests are mainly affected by extracurricular activities, such as courses or private lessons.