This 3-wave longitudinal study explored the complex ways in which students' motivation (motivational attitudes and beliefs), relationships with teachers (closeness, conflict, and dependency), and academic achievement (reading comprehension and math performance) inform one another from kindergarten through 6th grade. The sample included students (N = 1,267; 49.3% boys) and 207 teachers participating in the Dutch triennial COOL cohort study. At all waves, teachers reported on relationship quality and students' motivational attitudes, and students completed nationally normed reading comprehension and math tests. Students also reported on their motivational beliefs (self-efficacy and task motivation) and levels of closeness with their teachers at Waves 2 and 3. Cross-lagged panel models revealed robust support for 4 transactional models of teacher- and student-reported closeness, and teacher-reported conflict and dependency. These models generally indicated that student-teacher closeness, conflict and dependency, students' motivation, and academic achievement informed each other across the elementary grades.