Provider education programs that use academic detailing to improve childhood immunization have been implemented in several states. The purpose of this study was to evaluate the impact of these types of programs to improve immunization-related behaviors in private provider offices. The intervention included peer-based academic detailing in which teams of 1 physician, 1 nurse, and 1 office manager visited pediatric and family practices to deliver an educational presentation and develop practice-specific action plans. Comparison of pre-post intervention surveys showed that providers' willingness to give the maximum number of immunizations due at 1 visit (P < .001) increased. More providers reported routinely screening immunization records at sickness or injury visits (P < .05) and using minimum intervals (P < .001) postintervention. Mean change in baseline and postintervention overall scores was significant for pediatric practices (0.40, P < .05), small practices (0.64, P < .01), Vaccines for Children (VFC) practices (0.74, P < .05), and non-VFC provider practices (0.67, P < .01) but not for family or large practices.