Behavioral evidence indicates that skills associated with children's cognitive control (e.g., response inhibition and attentional control) undergo rapid development during early childhood. A particularly important time is the transition to elementary school. Yet, at present, relatively little is known about developmental changes in the brain processes linked to cognitive control during this period, including those associated with error monitoring, including the error-related negativity (ERN) and the error positivity (Pe). Moreover, understanding how ERP correlates of cognitive control relate to behavioral measures of these skills over time is also limited. In the present study, repeated assessments of 4- to 6-year-old children's (N‚Äâ=‚Äâ49, mean age‚Äâ=‚Äâ5 years 10 months) performance on a go/no-go task were collected to examine developmental changes in error processing and response inhibition across 6 months. Data revealed the presence of both the ERN and Pe at each time point, but also showed individual differences in the test-retest associations for each component. Behavioral changes in response inhibition on the go/no-go task and a standardized measure of attentional control were associated with changes in electrophysiological measures of error processing. Additional analyses comparing children of the same age who had completed the go/no-go task once to those who participated longitudinally revealed that, with repeated assessments, children exhibited behavioral changes in performance that could be attributed to both development and to the effects of practice, such as strategic accommodation.