This study investigates the associations between students' developmental changes in academic self-efficacy, academic initiative, and grade point average (GPA) during a three-year upper secondary education. The sample consisted of 1453 students aged 16-19 (60.6% girls; baseline mean age = 17.00, SD = 0.91; 56.1% high perceived family wealth; and 74.9% Norwegian-born). To explore how changes in academic self-efficacy, academic initiative, and GPA were related, we investigated a theoretical parallel process latent growth curve model. The results implied that, during upper secondary school, academic self-efficacy declined, while academic initiative and GPA remained stable. We found possible ceiling effects within and between several of the study's constructs. The main finding was support for a positive feedback loop between the developmental trajectories of academic self-efficacy, academic initiative, and GPA. The present study adds new insight that should be taken into consideration when promoting positive educational development during late secondary school.