Meritocratic ideology can promote system justification and inequalities perpetuation. The present research tests whether priming merit in the school context enhances the socioeconomic status (SES) achievement gap. Fifth graders read a text priming either school merit or a neutral content, reported their French and mathematics self-efficacy as well as their belief in school meritocracy (BSM), and then took French and mathematics tests. Compared to the neutral condition, the merit prime condition increased the SES achievement gap. Self-efficacy and BSM were tested as two potential mediators of the effect. The results support a mediated moderation model in which belief in school meritocracy is the mechanism through which the merit prime increased the SES achievement gap.