ImportanceMedical test overuse and resulting care cascades represent a costly, intractable problem associated with inadequate patient-clinician communication. One possible solution with potential for broader benefits is priming routine, high-quality medical test conversations.ObjectiveTo assess if a peer comparison and educational intervention for physicians and patients improved medical test conversations during annual visits.Design, Setting, and ParticipantsRandomized clinical trial and qualitative evaluation at an academic medical center conducted May 2021 to October 2022. Twenty primary care physicians (PCPs) were matched-pair randomized. For each physician, at least 10 patients with scheduled visits were enrolled. Data were analyzed from December 2022 to September 2023.InterventionsIn the intervention group, physicians received previsit emails that compared their low-value testing rates with those of peer PCPs and included point-of-care–accessible guidance on medical testing; patients received previsit educational materials via email and text message. Control group physicians and patients received general previsit preparation tips.Main outcomes and measuresThe primary patient outcome was the Shared Decision-Making Process survey (SDMP) score. Secondary patient outcomes included medical test knowledge and presence of test conversation. Outcomes were compared using linear regression models adjusted for patient age, gender, race and ethnicity, and education. Poststudy interviews with intervention group physicians and patients were also conducted.ResultsThere were 166 intervention group patients and 148 control group patients (mean [SD] patient age, 50.2 [15.3] years; 210 [66.9%] female; 246 [78.3%] non-Hispanic White). Most patients discussed at least 1 test with their physician (95.4% for intervention group; 98.3% for control group; difference, −2.9 percentage points; 95% CI, −7.0 to 1.2 percentage points). There were no statistically significant differences in SDMP scores (2.11 out of 4 for intervention group; 1.97 for control group; difference, 0.14; 95% CI, −0.25 to 0.54) and knowledge scores (2.74 vs 2.54 out of 4; difference, 0.19; 95% CI, −0.05 to 0.43). In poststudy interviews with 3 physicians and 16 patients, some physicians said the emails helped them reexamine their testing approach while others noted competing demands. Most patients said they trusted their physicians’ advice even when inconsistent with educational materials.Conclusions and RelevanceIn this randomized clinical trial of a physician-facing and patient-facing peer comparison and educational intervention, there was no significant improvement in medical test conversation quality during annual visits. These results suggest that future interventions to improve conversations and reduce overuse and cascades should further address physician adoption barriers and leverage patient-clinician relationships.Trial RegistrationClinicalTrials.gov Identifier: NCT04902664