The current study presents the results of two experiments designed to assess developmental change in post-error slowing (PES) across an age range extending from 5 to 25 years. Both experiments employed two-choice tasks and manipulated response-to-stimulus intervals (RSIs). The results showed that PES decreased with advancing age; a disproportional developmental trend was observed in experiment 2 while the age-related change in PES in experiment 1 was similar to the developmental decrease in basic response speed. In both experiments, age and RSI effects on PES did not interact. This pattern of results was interpreted to suggest that PES at long RSIs is due to increased caution and at short RSIs to a combination of increased caution and the time it takes to orient toward the error. The developmental change in PES at longer RSIs was interpreted to suggest that as children grow older they are becoming more effective in setting appropriate response thresholds.