High school teachers often struggle to engage students who have little or no motivation to learn. We argue that improving students' perceptions of affective relationships with teachers may have the potential to positively influence their motivation, and vice versa. This study looks at reciprocal associations between students' perceptions of the teacher-student relationship climate (PTSRC) and three components of academic motivation (autonomous, controlled, and amotivation), measured at two time points, over a 12-month period. We recruited 328 students (on average 15 years of age, 65% girls) from public high schools in disadvantaged areas of a Canadian suburb. We found that students' autonomous motivation predicted an increase in positive PTSRC. In contrast, we did not find evidence that PTSRC predicted either autonomous or controlled motivation. Nonetheless, a positive PTSRC predicted a decrease in students' amotivation. This finding suggests that high school students' positive PTSRC can help them find purpose in their schooling. Knowing that motivation typically declines during the high school years, this study is important because it suggests that promoting positive teacher-student relationships can contribute to ward off such decline.