We examined the differential outcomes in residential treatment for youths with conduct disorder (CD)—with special attention paid to interactions with age and gender—in a sample of children and adolescents in 50 residential treatment centers and group homes across Illinois. Multi-disciplinary teams rated youths ages 6–20 (N = 457) on measures of mental health and other factors within 30 days of admission, about 7 months after admission, and at discharge. While both groups initially responded similarly to treatment, the CD group performed better relative to the non-CD group over the full course of treatment, showing healthier relative change on five outcomes variables and more significant improvement. Age range moderated the relationship between CD group membership and change in work/school performance. There were significant between groups differences within the youngest age group (6–11 years) in which the CD group worsened relative to the non-CD group.