We used data from a randomized clinical trial to examine the degree to which relationship quality predicted outcomes for aggressive children in two different mentoring programs. Data were available for 145 aggressive children in Grades 2 and 3. Children were blocked by school and randomly assigned to PrimeTime (n = 75) or Lunch Buddy (n = 70) programs. PrimeTime combined community-based mentoring with child-focused skills training and consultation for parents and teachers, and mentors were extensively trained and supervised. Lunch Buddy was a stand-alone, school-based mentoring program that involved lunchtime visits and a different mentor each semester. PrimeTime children rated their mentors as more supportive than did Lunch Buddy children. Relationship conflict predicted changes in teacher-rated externalizing problems. Ratings of relationship quality interacted with treatment in predicting changes in parent-rated externalizing behavior for PrimeTime children only. (Contains 5 tables and 2 footnotes.)