Social anxiety is associated with reduced educational achievement. Given that concentration is a predictor of educational achievement, and social anxiety symptoms are associated with reduced concentration in class, this prospective study examined the possibility that social anxiety may impair educational achievement through reduced classroom concentration. A sample of 509 participants (53.8% female; M age: 12.77 years [SD = 0.81]) recruited from secondary schools completed questionnaires assessing social anxiety symptoms, depressive symptoms, and concentration in class. Educational achievement was assessed by internal grades within schools. An indirect effect of social anxiety on later educational achievement via concentration was observed, over and above baseline achievement and depression symptoms; adolescents with higher levels of social anxiety tend to have more difficulties concentrating in class, which in turn is associated with poorer academic outcomes. Findings underscore the challenges socially anxious adolescents will face trying to learn in school, and the need for education providers and clinicians to consider the effect of social anxiety symptoms on concentration and learning.