Adolescents typically exhibit a marked decline in academic intrinsic motivation throughout their school careers. Following self-determination theory, it is hypothesised that traditional school environments insufficiently satisfy three basic psychological needs of youths during maturation, namely the needs for autonomy, competence and relatedness. As a consequence, insufficient need satisfaction might account for the decline in intrinsic academic motivation during adolescence. This hypothesis was tested in an accelerated longitudinal cohort design on N = 600 students (286 girls) between 11 and 16 years of age. The results showed that students exhibited a marked decline in intrinsic motivation during adolescence. Moreover, differences in need satisfaction predicted the decline in motivations. These results support the notion that an adequate satisfaction of three basic psychological needs in school is crucial for the maintenance of intrinsic academic motivation during adolescence.