In school settings, sources of self-efficacy have the potential to directly and indirectly influence performance. The problem of this study is the direct relationship between sources of self-efficacy and achievement. In connection with this problem, the impact of sources of mathematics self-efficacy on high school senior students' mathematics test and course achievement was investigated. The study consisted of 257 12th-grade high school students. The findings of the study showed that mathematics course and test performance increased, whereas the scores for mastery experience, social persuasions, vicarious experience, and physiological state increased, too. According to the results of the regression analysis on mathematics course achievement, the mastery experience significantly predicted mathematics course performance. It also explained 56% of the total variance in mathematics achievement. On the contrary, mastery experience, social persuasions, and physiological state significantly predicted mathematics test achievement, as well as explained 27% of the total variance in mathematics test achievement. In conclusion, sources of mathematics self-efficacy have effects on both mathematics test and course achievement.