Epistemic cognition involves the thinking executed as people discern what they know versus what they question, doubt, or disbelieve. Effective or adaptive epistemic cognition underlies the higher-order thinking required for life in the 21st century and has been positively correlated with academic achievement. As such, researchers have designed a number of educational interventions with the goal of developing students' epistemic cognition, but no comprehensive examination of their efficacy exists. Therefore, we conducted a meta-analysis to better understand the effect of epistemic cognition interventions upon academic achievement and what characteristics differentiated their efficacy. Twenty-six experimental and quasi-experimental studies met our inclusion criteria. Using 28 independent samples and 59 effect sizes, we found epistemic cognition interventions had a statistically significant, medium-level effect on academic achievement (Cohen's d = 0.509, p < 0.001). Moderator analyses revealed interventions based in guided forms of instruction and models emphasizing justification and reconciliation of objectivity and subjectivity were more successful than other interventions, suggesting several promising directions for future research and practice. Surprisingly, we found that shorter interventions were generally more successful in promoting academic performance than longer ones.