In academic contexts, failure, as compared to success, is likely to threaten self-esteem and thus, to increase the risk of psychological disengagement from one's studies. The goal of the present research is to examine whether belief in school meritocracy (BSM) increases (vs. decreases) the effect of academic performance on self-esteem and psychological disengagement. In two pre-registered studies, university students reported their BSM. Their self-esteem and psychological disengagement were assessed following a manipulated (Study 1, N = 465) or actual (Study 2, N = 375) academic performance. Results indicated that, in both studies, BSM was positively related to performance self-esteem and negatively related to psychological disengagement. However, BSM also increased the effect of performance (manipulated or actual) on psychological disengagement. Indeed, failure led to more disengagement than success, but more so at a high level of BSM than at a lower level of BSM. The double-edge effects of belief in meritocracy are discussed.