This study examined children's trajectories of mathematics and reading achievements from kindergarten to eighth grade along with the gender differences in these trajectories. A total of 8503 participants drawn from the Early Childhood Longitudinal Study-Kindergarten Cohort (ECLS-K) formed the sample of the study. The results of the latent growth curve modeling indicate that (a) children's growth is curvilinear, specially, quadratic for both mathematics and reading achievement, and their growth in reading demonstrate a more complex pattern than that of mathematics; (b) there appear to be positive correlations between the intercept parameter (i.e. initial status) and the slope parameter (i.e. growth rate) in both reading and mathematics trajectories, indicating the "Matthew effects" in education; (c) despite the statistically equivalent initial status in mathematics, boys outperform girls as early as first grade in both achievement score and positive growth rate; (d) for reading trajectories, girls outperform boys in both initial status and positive growth rate starting the baseline measurement. Finally, limitations and recommendations for future studies are discussed.