Objective: To test whether adoption of a collaborative consultative service model results in improved patient outcomes. Design: Twelve pediatric practices were randomly assigned to receive access to collaborative consultative services or to a control group. Setting: Community-based pediatric offices. Participants: Fifty-two pediatricians and their 377 patients with attention-deficit/hyperactivity disorder ( ADHD). Intervention: A collaborative consultative service promoting the use of titration trials and periodic monitoring during medication maintenance. Main Outcome Measure: Physician practice behaviors and child ADHD symptomatology. Results: Using self-report of pediatricians, the collaborative consultative service increased the use of evidencebased practices by pediatricians, but no difference in children's ADHD symptomatology was observed between the groups. However, many pediatricians did not fully use the collaborative consultative services. Those children who actually received collaborative consultative services showed significant behavioral improvement compared with children not receiving these services. Conclusions: When actually implemented by pediatricians, the collaborative consultative service appears to be an effective method for facilitating evidence-based treatment procedures for ADHD and use of these procedures appear to improve children's outcomes. Barriers to implementation of collaborative consultative service in pediatric practice need to be further understood.