Internal dynamics of school engagement and their impact on educational attainment have been studied scarcely. Understanding these processes is crucial, particularly in view of declining school engagement across adolescent years. This study examines dynamic interrelations of motivational and behavioral engagement components across mid-childhood and mid-adolescence. We analyze how levels and changes of academic interest and effortful engagement interact and scrutinize their co-development for its impact on educational attainment in a tracked school system. Structural equation models based on ten-year six-wave Swiss longitudinal data show that academic interest triggers a feedback loop with effortful engagement gradually leading towards differential educational attainment.