It has been suggested for many years that students who are able to judge their own performance should do well in academic assessments. Despite the increasing number of empirical studies investigating the effect of self-assessment on academic performance, there has not been a recent synthesis of findings in the higher education context. The current meta-analysis aims to synthesise the effects of self-assessment on academic performance. In particular, it examines the difference between situations in which the process of self-assessment is revealed or observable (explicit) or not revealed or unobservable (implicit). A total of 98 effect sizes from 26 studies either reported a comparison between a group with self-assessment interventions and a control group (n = 20, k = 88) or a pre-post comparison (n = 6, k = 10). The overall effect of such interventions was significant (g = .455). Self-assessment interventions involving explicit feedback from others on students' performance had a significantly larger effect size (g = .664) than those without explicit feedback (g = .213). There were no other significant moderators identified for either the overall effect or the effect of interventions involving explicit feedback. Supplemental data for this article is available online at http://dx.doi.org/10.1080/02602938.2021.2012644 .