This paper shows that an aspirations failure reinforces social inequalities at school. We find evidence that aspirations affect later school outcomes and that social inequalities in aspirations exist even among equally-achieving classmates. The main reason for the latter is that equally-achieving classmates of different social origins do not feel capable of pursuing the same academic tracks. Importantly, this difference is partly explained by social stereotypes: students exhibit excessive social fatalism and the low-SES underestimate their present academic capacity compared to the high-SES. These findings provide evidence of inefficiencies in teenagers' aspirations and validate Ray's model of an aspiration-based poverty trap.