In this study, by using the hypotheses of social-cognitive career theory (SCCT), the relationship between informative sources of math-related self-efficacy expectations and self-efficacy, interest, and math-weighted major preferences were investigated. The participants in this study were students (N=590) from high schools in Southern Turkey. Participants completed measures of sources of math-related self-efficacy, self-efficacy, interest, and choice consideration related to math-weighted majors. While running analyses, sampling was split in half at random and psychometric analyses of the scales were run with the first half (n=298); the second half (n=292) was used to test the hypotheses. By doing this, the testing of hypotheses would not be affected by just one specific sampling characteristic. A structural equation model was tested and findings indicated general support for hypotheses that these sources predict self-efficacy beliefs and these beliefs also predict interest. However, contrary to SCCT's predictions, math-weighted major preferences are not predicted by math-related self-efficacy expectations and interest. In the Discussion, first, the reasons why the measurement of vicarious learning or modelling did not significantly predict self-efficacy expectations focus on the relationships between personal accomplishments and persuasion and reported physiological arousal and personal accomplishments. Some information is given as to how counsellors and math teachers can work collaboratively to raise perceptions about informative sources. Second, explanations are given about why self-efficacy and interest did not predict math-weighted preferences. It is mentioned that this could be the reason for the constrained and complex system of the university entrance exams and placement in Turkey. The importance of investigating environmental variables on SCCT in developing countries was emphasized. Suggestions are also given for further research. It is concluded that this theory should be tested in developing countries like Turkey.