In recent years, there has been much interest regarding motivation and its effect on achievement patterns. When students enjoy learning, they are more likely to show interest, value, and effort toward achievement, perform well, and persist in school (e.g., Vallerand et al., 1989). The purpose of the study is to develop and test a model, based on Self-Determination Theory (SDT). The model incorporates the assumption that intrinsic motivation positively affects math performance, whereas external regulation negatively affects math performance. It is assumed that math self-concept affects math performance both directly and indirectly through the mediating variable of intrinsic motivation. Finally, autonomy support can affect math performance both directly and indirectly through the mediator of math self-concept. Consistent with the predictions of SDT, when teachers support autonomy of students in the classroom, they provide a classroom climate that fosters math achievement. As teachers try to support students' competencies, they are more likely to foster students' self-perceptions of competence, which, in turn, promotes math achievement.