Adaptive expertise helps physicians apply their skills to novel clinical cases and reduce preventable errors. Error management training (EMT) has been shown to improve adaptive expertise with procedural skills; however, its application to cognitive skills in medical education is unclear. To evaluate whether EMT improves adaptive expertise when learning the cognitive skill of head computed tomography (CT) interpretation. This 3-arm randomized clinical trial was conducted from July 8, 2022, to March 30, 2023, in 7 geographically diverse emergency medicine residency programs. Participants were postgraduate year 1 through 4 emergency medicine residents masked to the hypothesis. Participants were randomized 1:1:1 to a difficult EMT, easy EMT, or error avoidance training (EAT) control learning strategy for completing an online head CT curriculum. Both EMT cohorts received no didactic instruction before scrolling through head CT cases, whereas the EAT group did. The difficult EMT cohort answered difficult questions about the teaching cases, leading to errors, whereas the easy EMT cohort answered easy questions, leading to fewer errors. All 3 cohorts used the same cases. The primary outcome was a difference in adaptive expertise among the 3 cohorts, as measured using a head CT posttest. Secondary outcomes were (1) differences in routine expertise, (2) whether the quantity of errors during training mediated differences in adaptive expertise, and (3) the interaction between prior residency training and the learning strategies. Among 212 randomized participants (mean [SD] age, 28.8 [2.0] years; 107 men [50.5%]), 70 were allocated to the difficult EMT, 71 to the easy EMT, and 71 to the EAT control cohorts; 150 participants (70.8%) completed the posttest. The difficult EMT cohort outperformed both the easy EMT and EAT cohorts on adaptive expertise cases (60.6% [95% CI, 56.1%-65.1%] vs 45.2% [95% CI, 39.9%-50.6%], vs 40.9% [95% CI, 36.0%-45.7%], respectively; P < .001), with a large effect size (η2 = 0.19). There was no significant difference in routine expertise. The difficult EMT cohort made more errors during training than the easy EMT cohort. Mediation analysis showed that the number of errors during training explained 87.2% of the difficult EMT learning strategy's effect on improving adaptive expertise (P = .01). The difficult EMT learning strategy was more effective in improving adaptive expertise for residents earlier in training, with a large effect size (η2 = 0.25; P = .002). In this randomized clinical trial, the findings show that EMT is an effective method to develop physicians' adaptive expertise with cognitive skills. ClinicalTrials.gov Identifier: NCT05284838.