While teacher expectations are known to influence students’ academic achievement, they may also exert significant influences on student motivation, which is a precursor to a student’s achievement as well. A number of previous studies have demonstrated that motivation affects a student’s achievement. There is, however, a dearth of longitudinal research examining the relation between teacher expectations and students’ motivational variables. In this article, we examine the relations between teacher expectations of students’ mathematics ability, students’ mathematics-related competence beliefs, and students’ mathematics-related intrinsic task-values. Our sample consisted of 796 second-grade students and their 50 teachers; the data collection was conducted at three points within a school year. Longitudinal latent change score analyses yielded three main results: First, teacher expectations of students’ mathematics ability and both students’ mathematics-related competence beliefs and intrinsic task values decreased significantly in the second half of the school year. Second, regarding correlated changes, students who experienced larger increases in teacher expectations also demonstrated higher increases in competence beliefs and intrinsic task values in mathematics. Third, after controlling for students’ initial mathematics achievement, effects of teacher expectations of students’ mathematics ability at the beginning of the school year on subsequent changes in students’ mathematics-related competence beliefs and intrinsic task values were revealed. Our study highlights the important role of teacher expectations in shaping students’ motivational variables, which underscores the need for teacher training programs and policy interventions aimed at increasing teachers’ awareness of their expectations and how they can foster a positive learning environment for their students.