To determine the effects of self-concept, attitude, and interest on the math performance of 21082 eight graders participating in four TIMSS studies from 2003-2015, and the trend of these effects, factor analysis, effect size, and structural modeling were utilized. Findings indicate that self-concept can predict math performance, both directly and indirectly, followed by interest and attitude. However, the latter two have a negative impact on performance which calls for further studies to determine the reasons. As for the trends of these effects, data analyses show that the changes in performance, and in the three variables, are not unidirectional. From 2003 to 2007, despite an increase in self-concept and attitude scores, the average performance score has decreased. Within the 2007-2011 period the performance score has increased while the scores on self-concept and interest in math have decreased. Within the third interval, in spite of increase in performance score, the scores on all three other variables show a decrease.