<p>There is growing interest in how contextual factors influence student motivation, with the teacher playing a key role in the classroom environment. This study examines the contribution of perceived teacher support to student motivation and achievement in mathematics. A sample of 518 ninth-grade students was assessed three times within a school year. Participants reported (i) their perceptions of instrumental and emotional support provided by their mathematics teachers (Time 1), (ii) their expectancies of success, subjective value and perceived cost in relation to mathematics (Time 1 and Time 3), and (iii) their mid-year mathematics grades (Time 2). Structural equation modeling indicated that both forms of perceived teacher support early in the school year had sustained associations with students’ expectancy beliefs, value and cost through the spring. Moreover, perceived instrumental and emotional support positively predicted later mathematics achievement indirectly, via students’ expectancy beliefs. Cost also emerged as a significant mediator between teacher’s perceived instrumental support and students’ later subjective value of mathematics. These findings highlight the important role of perceived teacher support in sustaining student motivation throughout the school year and provide further insights into the conceptual relationship between perceived cost and subjective task value. Implications for educational practice are discussed.</p>