Comparing health risks is challenging. We tested whether a worked-example intervention with number line (NL) visual displays improved adults’ risk comparison accuracy, whether pretest confidence moderated learning, and which individual differences related to accuracy. Replicating prior work, U.S. adults randomly assigned to the intervention (n = 883) were more accurate than control participants (n = 949) at solving health-related math problems with number line visual displays and a transfer problem without a visual display. One day later, most participants were accurate and there were no differences between conditions, potentially because participants with better math skills and attitudes participated at follow-up. However, there was a small effect on accuracy 1 day later among those who learned from the intervention. Adults were more likely to learn from the intervention if they made a low-confidence pretest error. Identifying as male, accurately estimating numbers on number lines, lower math anxiety, higher educational attainment, and being older were associated with greater risk comparison accuracy.