The directionality and longitudinal course between perfectionism and academic achievement throughout adolescence remains unclear as most studies rely on cross-sectional or short-term data and many examine these associations in university students who do not represent the full spectrum of learners. Moreover, most studies are hampered by their reliance on student-reported grades. We rectified these issues by examining the longitudinal relation between self-reported perfectionism and teacher-rated academic achievement (grade point average) in a sample of 604 Canadian adolescents followed prospectively from Grade 7 to Grade 12. Using path analysis, results demonstrated a positive relation between academic achievement and perfectionism. In particular, academic achievement positively predicted self-oriented perfectionism (SOP) at every time point. Academic achievement also positively predicted socially prescribed perfectionism across every time point. At no time point did either form of perfectionism predict academic achievement, highlighting that perfectionism is more likely an outcome of academic achievement, rather than an antecedent. Results also demonstrated that the cross-lagged effect from academic achievement to SOP was stronger at the transition from middle school to high school compared to pathways in all subsequent years. Overall, such findings imply that adolescents who experience academic success are more likely to experience increases in levels of perfectionism, which may increase their vulnerability to stress.