A theoretical model linking boredom and academic achievement is proposed. Based on Pekrun's (2006) control-value theory of achievement emotions, the model posits that boredom and achievement reciprocally influence each other over time. Data from a longitudinal study with college students (N = 424) were used to examine the hypothesized effects. The study involved 5 assessments of students' boredom and test performance during a university course spanning an entire academic year. Structural equation modeling was used to examine effects of boredom on achievement, and vice versa. The results show that boredom had consistently negative effects on subsequent performance, and performance had consistently negative effects on subsequent boredom, while controlling for students' gender, age, interest, intrinsic motivation, and prior achievement. These results provide robust evidence for the proposed links between boredom and achievement and support systems-theoretical perspectives on the dynamics of emotions and achievement. From a broader educational perspective, the findings imply that researchers and practitioners alike should focus attention on boredom as an important, yet often overlooked, academic emotion.