Achievement emotions have received increasing attention in research on adolescence and young adulthood, but little is known about these emotions in the early years of schooling. Studies addressing the development of different achievement emotions and their linkages with achievement during these years are largely lacking. The present longitudinal study aimed to fill this gap by examining the development of enjoyment, boredom, and anxiety in mathematics across second to fourth grade (N = 670 German students; Mage = 8.45 years, 51.0% female at baseline) as well as relations between these emotions and children's math achievement. Students' emotions during learning and when taking tests and exams in math, school grades in math, and math achievement test scores were measured in annual assessments. Latent structural equation modeling showed that enjoyment decreased, whereas boredom and anxiety remained relatively stable across these years. Moreover, the findings from reciprocal effects models (REMs) show that emotions and achievement were reciprocally linked over time, controlling for autoregressive effects, gender, and family socioeconomic status. Enjoyment positively predicted subsequent achievement, and achievement positively predicted subsequent enjoyment. Boredom and anxiety negatively predicted subsequent achievement, and achievement negatively predicted subsequent boredom and anxiety. The results were consistent across waves and achievement indicators and highlight the need to attend to students' achievement emotions during the early years of schooling. Directions for future research and implications for educational practice are discussed.