The purpose of the present study was to examine the effects of student-related variables on achievement in mathematics. The sample consisted of 3736 13-year-old Jordanian 8th-graders who participated in the Third International Mathematics and Science Study (TIMSS). The participants completed a student questionnaire and participated in the mathematics test. Of the matrix of affective variables reported to lead to the variation in mathematics achievement were educational aspiration, attitude, success attribution, confidence in ability and perception of importance of mathematics. A structural equation model was used to estimate and test the hypothesized relationships of the factors with achievement in mathematics. Results from this study indicate that four attitudinal and motivational variables had strong positive total and direct effects; and two variables had negative total and direct effects on mathematics achievement. Recommendations for future research were suggested.