School engagement is an important theoretical and practical cornerstone to the promotion of academic accomplishments. This article used a tripartite—behavioral, emotional, and cognitive—model of school engagement to assess the relationship between school engagement and academic success among high school students, and to determine whether a reciprocal relationship exists between these constructs. Data were derived from 710 youth (69 % female) who took part in Waves 6 through 8 (Grades 10 through 12) of the 4-H study of positive youth development. Longitudinal confirmatory factor analyses confirmed the invariance of the tripartite model of school engagement. Results of a structural equation model showed that the components of school engagement and academic achievement were mutually predictive and that these predictions varied from grade to grade. Future possibilities for evaluating the relationship between school engagement and academic achievement, as well as the implications for educational policy and practice, are discussed.